Bridges, Tunnels, Complex Structures – Engineering for Kids


In the first week of our Engineering Unit, we studied Towers – stacking one block on top of another block to build something tall. This week, we looked more at more complex structures. We played with bridges, tunnels, beaver dams and more.

Concept Exploration – the best activities

Index card bridges: We had a table with blocks, index cards, and glass stones. As children came in, we would demonstrate three types of bridges to them and tested how many “stones” it would hold. (We got this idea from Stay at Home Educator – be sure to check out her photos, which are much better illustrations than my diagrams!) We showed them:

beam     arch     accordion

  1. Beam bridge – set two blocks up, put an index card spanning the distance between them. That will hold just three stones (unless kids were clever enough to rest the stones directly on top of the blocks rather than in the middle of the index card bridge)
  2. Arch bridge – insert one index card BETWEEN the two blocks, to form a support arch, then lay another index card on top of it for the flat bridge deck. That generally would support 7 stones.
  3. Accordion beam: take two index cards – fan fold them. Lay those on the two blocks, then put a flat index card deck on top of them. That would easily hold 20 or so stones.
We would demonstrate these three ideas, then challenge them to test as many other ideas as they could come up with. We walked away and let them tinker, exploring different materials and ways of using them in order to build stronger bridges. Our littler kids just played with the basics of bridges. Our older ones really took in more of the message about testing different methods. I only caught a few pictures of the process, but you can see a variety of methods were explored.
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Marshmallow Structures: We put out mini marshmallows, big marshmallows, and toothpicks for kids to build whatever they wanted with. (Note: kids will want to eat the marshmallows. For some of my kids, I didn’t bring it up unless they asked. Others, I knew I had to pre-empt. One I told on the way in that he could eat one marshmallow at the start of class and one marshmallow at the end of class and that was all – I knew if I gave that permission up front, he would absolutely eat those two, but that would be it. A mischievous little girl was eating marshmallows in front of me, as I told her not to, and I told her that if she continued, I would send her away from the table, so she ate one more, and I did. But it wasn’t really a punishment from me – it was her way of testing and accepting her limits.)
You can also do this activity with gum drops instead of marshmallows – they actually work a little better. Or, you can choose healthy items, and this can be the snack: first they build their building, then they eat it! You could use apple cubes, grapes, cheese cubes, or other food for this activity. One of the things I like about this project is that kids discover the strength of the triangle, and build trusses to support their structures.
Photos from, little bins for little hands,, and Artful Parent.

Big blocks. It’s just fun to build with really big blocks – these are heavy and moving them around feels like an accomplishment. You have to warn the kids not to knock structures over and to be very careful when building up, because these blocks are really heavy and really hurt if a corner of one falls on your toes! You could also use cereal boxes and cracker boxes as big blocks.

FIL 015  FIL 057

Note, if you have access to big blocks (wood, foam, or cardboard) I love the idea from Not Just Cute of taping out a pattern of blocks on the wall and having kids match that pattern.

Tunnels in the Sensory Tub. We made a cloud dough with flour, cocoa powder and vegetable oil. It smells good, it’s somewhat moldable (like kinetic sand), it looks like dirt, and it won’t hurt you if you eat it. Last year, we placed it in the tub with rocks, dishes, and tongue depressors, so children could build bridges and tunnels. This year, we used curved arch blocks, and other blocks, plus added a picture of a few ways to build tunnels.
IMG_20160227_142512032   img_20161001_100228157  covered-tunnel   cut-and-cover-tunnel
Building a Wind-Proof Structure. In the IMAX movie Dream Big,  they showed a classroom project where kids were given paper or cardstock, and told to build a building that would withstand the wind. Then they tested them by placing them in front of a large fan (like the one we use for our wind tube), starting on the low setting, then adding more and more wind to see whether they could withstand it or would topple.
Concept Exploration – other ideas
As we create our own curriculum, we come up with some activities that are fabulous. They meet all this criteria: fun, educational, adapt to a variety of ages and interest, and easy for us to set up and clean up. And sometimes we have some activities that are OK… but not fabulous – they may miss on some of those criteria. Here are a few we weren’t as happy with from last year and this year… They’re still good activities, but not great. So, we’ll be refining and/or replacing them in future classes.
Pipe cleaners and straws: Kids could thread pipe cleaners through cut up straws, and then bend into various structures. (Idea from Meaningful Mama.)
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I really liked this idea. I figured the three year olds would just enjoy sticking pipe cleaners through straws, our four and five year olds might make two dimensional shapes, and our six and seven year olds might make three dimensional shapes. The first year, the materials didn’t really capture kids’ imagination, so this year, I put out a poster showing lots of examples of shapes they could make, and it still didn’t really engage any kids for very long. It might work better as a collaborative building project, like in this post from the Map is Not the Territory where they make interconnected cubes.
Another idea: Learning Resources has a Dive into Shapes, “Sea” and Build Geometry Set which looks like a fun toy for building structures. We chose not to get it for class because we prefer using materials that anyone can have at home to empower them to tinker at home, rather than purchasing specialty equipment. But you might want to check this out.
Water table – We had toy boats in the water table, and items to build bridges with to sail the boats under. I’m thinking about what building materials will be best for bridge building here, but haven’t come up with the best solution yet. (The challenge with building in the water table is that some building materials are damaged by water, and many building materials (e.g. Duplos) just float away!
Arch Bridge.  I made salt dough (1/2 cup salt, 1 cup flour, ~1 cup water), formed an arch, VERY carefully cut it into slices and baked it (250 for 2 hours). I was hoping it might be a stand-up arch bridge. It wasn’t. The pieces expanded just a little when cooking, but it was enough to distort the shapes so the bases would not stand. We did use it in class, but instead of being a cool upright structure, it was a math activity of put the pieces in order by number to make an arch. (We had a picture of a Roman arch bridge next to it so they saw what it related to.)


There are a few kits available of roman arches: Haba Roman Arch,
Our Amazing Bridges Model Building Kit, or the more expensive
Montessori Roman Arch. We generally try to build most of our own materials rather than buying specialty products, but this may be one of those places that’s worth buying a product someone else has engineered.

Igloos. We built igloos with sugar cubes and glue. Here’s the beginning of one. Place a good illustration of igloo building next to this for guidance. (Preschool age kids need to have context. Even if they’ve seen an igloo before, they may not be able to pull up an image of it just by you saying the word igloo. Having the picture helps them really grasp what you’re talking about. Next year, we plan to use icing instead of glue to “mortar” the pieces together


Nature / Imagination

We’re planning spring quarter as a Biology / Inventions unit, where we talk about things from nature and biology and also talk about how that inspires human builders and inventors. This week, we brought in the idea of an animal that builds structures.

Beaver Masks: Teacher Cym designed beaver masks on paper plates, and cut them out. In class, kids could decorate them.


Be a beaver: We built a set of tongs with paint stirrers, and kids could pretend that was their beaver mouth, and move around “sticks” made with newspaper rolls to build a dam.


Build a beaver dam: Last year, we put out paste (glue and flour mixed), spaghetti sticks, and “pebbles” (split peas and lentils) for kids to sculpt a beaver lodge or dam. This year, we used playdough, pretzel sticks, and pretzel rods.We had an illustration of a beaver dam nearby – again, the picture gives context and helps kids really understand the idea.

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Big Motor Play – Trusses and PVC pipes

I’d found a blog post on Modern Parents, Messy Kids that showed how to build what they called “Life Size Building Blocks” – triangular trusses made from newspaper. To make the paper tubes, they recommend “Take two sheets of newspaper, lay them out flat and start rolling it from one corner.” The advantage of this method is it’s quick and easy, and you need just one little square of tape to fasten each one. Their 7 and 9 year old were able to roll these by themselves. When I made my rolls, I made 45 (enough for 15 triangles) in the time it took us to watch Kung Fu Panda. But – the ends of these are very thin – that means they’re easy to staple together, but they also are weak and floppy and can collapse in on themselves. So, my husband developed a new method. Take two pieces of paper, and off-set them a bit. Then lay those two diagonally across a third. Roll from there. This results in ends that are still thin enough to be stapled, but sturdier than the basic method.

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This method was a little slower. My husband and I working together probably rolled about 45 in the time it took us to watch Little Mermaid.

In the blog post, they say their 7 and 9 year old did all the assembly. In our class, the parents did the assembly, using duct tape to fasten the joints, then the kids played in the big structure we had built.

IMG_20160227_112041955  IMG_20160227_113646090

In the book Build It: Invent New Structures and Contraptions, there are more detailed instructions on how to build a free-standing geodesic dome with newspaper trusses. It looks to be about 4 feet tall and 8 – 10 feet across.

This year, instead of the newspaper trusses, we used PVC pipe to build with. We had 3/4″ PVC in 2.5 foot, 2 foot, and 1 foot lengths, and we had lots of joints – T’s, elbows, couplers, and 3 way connectors. Kids and parents worked together to build a variety of structures. As often happens, I was busy building with kids, and didn’t get any photos of any finished projects, but here’s some in progress.


Circle Time

Bridges – Key concepts: We handed around several pictures of different types of bridges, and then we asked why people build bridges. Reasons included: to go across water without having to swim or get wet, to go across a valley without having to go down the hill and up the hill (think railroad trestle), to go over a road (highway overpasses and pedestrian bridges). Different obstacles present different challenges. For example, the log across the stream works great, but what if the water you want to bridge is wider than any log you have? Building a bridge on pilings is great, but if the water is REALLY deep, that doesn’t work. (We have floating bridges in Seattle that all our kids are very familiar with.)

So we need to be able to build bridges with a variety of materials and a variety of methods. We asked them about their experience with building bridges with blocks and index cards – it’s all the same materials, but the construction methods make a big difference. We also talked about materials – asking if it would be better to build a bridge from paper or wood, or from plastic or metal.

Book: We read Cross a bridge, a nice age-appropriate, engaging non-fiction on bridges.

Suspension bridge: Last year, we demo’ed a simple suspension bridge, built with a cardboard deck, string, and paper clips. This year’s bridge was more sophisticated.

If you’re working with 10 – 12 year olds, try this suspension bridge project.

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Demo: What shape holds the most weight: Take four pieces of paper. Fold one in half to make a tent. Fold one into a triangle tower, one into a squat square, and one into a round column. (Option: you could add in a paper cube with trusses.) Ask your child which will hold the most weight, then test them. Watch this video from PBS’ Zoom to see this demo in action, except… they use a heavy book each time which crushes three out of four shapes. I would start with a thin lightweight book, which would crush the tent, but maybe not the triangle or the square. Then test the heavier book on that shape – it will crush it. Then test light book on round column, then heavy book. We made a round column with construction paper that held 20 or so paperback books, then made a round column from a half sheet of cardstock (i.e. a 5.5 x 8.5″ piece of cardstock) and started stacking books on it. We got to 42 books before it collapsed!!

Song: Teacher Cym wrote a song to the tune of “Johnny Comes Marching Home Again”

We’re going to build a bridge today, hurray! hurray!
We’re going to build a bridge today, hurray! hurray!
We’ll make it strong, we’ll make it straight,
We’ll see if it will hold the weight,
And we’ll all be learning together while we play.

Closing Circle: For the older kids (age 4 – 7), we read Iggy Peck, Architect, which is a delightful story of a boy who likes to build, who is discouraged by his teacher, until he saves the day by guiding his class in building a suspension bridge from shoelaces, fruit roll-ups and things. For the little kids (age 3), we read I Build with Blocks this year, but I prefer last year’s book, which was The Bridge Is Up, a nice cumulative read-along about all the vehicles who have to wait while the draw bridge is up. Then we taught them the rhyme Zoom Down the Freeway. (the lyrics on this page and the hand motions are the same we use, but I say it as a rhyme instead of singing it to the tune he uses.) Many of the parents and kids learned this rhyme in our toddler class, and recognized it from there.

We also read London Bridge Is Falling Down which includes all the verses of the song, illustrated, plus music notation, plus (for adults or older kids) a section on the history of London Bridge. We read/sang it – it’s an old nursery rhyme, so the verses are a little odd in places… for example, they’ve put a guard on the bridge they need to keep awake, so the verse is “give him a pipe to smoke all night.”

After reading that, we played London Bridge. I like to bring in classic kids’ games where we can, and this was a nice opportunity. Two children make an arch, the rest of the kids line up and start going under the arch, then circling around to go under again. We sing the song, and whenever we get to “my fair lady”, the bridges drop their arms and capture someone, who then replaces one of the bridge supports and the game begins again.

More books:

Bridges: Amazing Structures to Design, Build & Test is aimed at much older kids, but has some fun ideas for advanced bridge building projects.

Dig a Tunnel is a engaging preschool read about tunnels. Digging Tunnels and Tunnels are also fine non-fiction choices, but Dig a Tunnel is my favorite of the 3.

Monsters Under Bridges. I wanted to love this book, a guidebook to the bridges of the Pacific Northwest. I only know one of these bridges well, but when I looked at those pages, they were not what I hoped for. In Seattle, under highway 99, we have a statue known as the Fremont troll. Where it appears in the book, it is mentioned as being one of many imaginary monsters here. I’d rather they just talked about the Fremont troll and made it “real” instead of making up others that aren’t here.

Look at That Building!: A First Book of Structures. A nice story that introduces fundamentals of buildings, like foundations, beams and frames. Too long to use in circle time, but worth a read.

Bridges Are to Cross. Very nice artwork depicting famous bridges around the world. Each page has a description of what bridges are for: “some carry llamas loaded with firewood across deep canyons, this bridge lets boats float under the road”. Has more details on each type of bridge in fine print. A fine book for the shelf.

[affiliate links – learn about all these books on Amazon and buy if you choose, but remember most of these can be checked out from your library!]

Videos to Preview or Review the Lesson. For 3 – 5 year olds, Peep and the Big Wide World: Bridge the Gap. For 4 – 6 year olds, What Make Bridges So Strong? (3:44). For 6 and up: Bill Nye’s Structures episode.

Resources for More Info on Bridges

PBS Building Big:

Links to more ideas:

Note: All the activities described in my posts are from Family Inventor’s Lab, a parent-child cooperative class in Bellevue, WA. We are a play-based, STEM focused class for preschool through early elementary (kids age 3 – 7). We do a wide variety of fun, hands-on activities to learn about Science, Tools, Engineering, Nature, and Art. We also sing songs and read stories. Most of our activities are cheap, easy, and use everyday materials that most families would have in their homes (or their recycle bins!), so that our activities are appropriate for classroom teachers, parents who homeschool, or after school programs.


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