Lego STEM Activities for a Preschooler

Dave | Updated June 8, 2021 |

Surviving extended periods of time at home and keeping your sanity is tough with young active and inquisitive children. When daycare, grandparents and activity clubs are all gone, what do you do? Raining outside too? Kids need something to entertain them. If they get bored, that’s usually when irritable or attention seeking behavior can set in. 

This year I decided I’d make a point of making ‘Daddy Time’ with my preschooler a little more structured (but no less fun) with a series of activities that I thought would keep both of us interested. Not only that but also that would throw a bit of STEM style education into the mix (more on that in a bit) and teach my little cub something about how stuff works

LEGO is great for this, it’s a popular gift for toddlers and you’re invariably going to end up with a lot of it lying around your house. You can make a lot of interesting things other than simple buildings or walls. However, sometimes this requires a little lateral thinking and planning ahead. Making contraptions that are going to be fun and exciting enough for a preschooler to help with adds another little puzzle into the mix.

With that in mind I went in search of ideas, made a list and then let my son pick what we did  from it each time he was ready for a little LEGO challenge. 

We enjoyed everything we did, I was surprised how involved he became and how pleased he was to show off to his mom what we’d achieved that day! Our favorites were the erupting volcano (very exciting, watch the vid later on!) and the frozen minifigures. But they were all fun.

Who needs to buy a marble run… make one!

I recorded our results and took some photos and videos each time and they’re all below. We didn’t get through everything this summer and I plan to do more next year. Here is our list of tried and tested ideas that should help out next time you’re at a loose end and have a few hours on a rainy holiday day to fill!

What’s STEM and Why?

STEM is an educational initiative that’s designed to focus and improve the learning of children in 4 key areas Science Technology Engineering and Maths. The thinking being that these subjects are more key to understanding, living and working in the modern world than ever before. 

Some might argue that actually music, art, literature and language are far more important. But I’m not going to get into that here. 

Whichever way you lean, it doesn’t really matter. Thinking about things, whatever they are, and working together with your parents to achieve something is fun. It’s empowering for your child. It’s interesting for both of you, teaches a little something and strengthens your bond!

With STEM activities the process of working together is just as important as the end result. It’s important you encourage your child to think and figure things out for themselves.

Most families have a box or a bucket of assorted LEGO somewhere!

Exploding LEGO Targets

Most of the time NERF guns in the hands of preschoolers are a recipe for disaster. That’s why I thought actually giving mine something fun to shoot at might work wonders. Something he could actually break without fear of recrimination!

Take a look at this roundup of the best NERF guns for toddlers if you’re interested in which NERFs and alternatives we’d recommend, ones that are easy to prime by little hands without you getting involved!

Loosely put together and explodes in style!

It turns out if you build pretty much any LEGO structure and don’t push the bricks together, you can create some things that explode in pretty spectacular ways when hit with a NERF bullet. The explosions are harmless, bricks go everywhere, it’s fun.

Where’s the educational value in this? Well maybe understanding how LEGO works. If you don’t push the pieces together properly they have no strength. You could try building 2 different walls, one properly with fitted pieces, and one loosely. Compare what happens when you hit them.

What you’ll need: 

  • A NERF gun or some other child friendly projectile like a small ball to throw if you don’t have one
  • LEGO bricks! 

Lego Marble Drop

Who doesn’t love watching a little ball bounce down a path, round a corner and into a hole? Pachinko anyone? Ever been entranced by a viral youtube video of a ping-pong ball? I know I have!

Here’s our finished marble drop!

What you’ll need: 

  • A tall LEGO baseplate (or several you can fix together to create a tower shape).
  • A marble or small ball
  • A box of regular LEGO or DUPLO bricks

This one was satisfying to get complete. A little tricky at times to have to adjust the position of the pieces when the ball didn’t go exactly where you expected. But this gives you a good opportunity to explain to your little one exactly what it is you need to do and why. How the ball will move, how you need to stop it, redirect it and get it down the path you want.

There are few little sub-tasks in this you can hand-off to them if you need a distraction whilst you tinker. One is to get them to build (or find) something that the ball is going to end up in (we built a lego pot). Also to devise a way to stop the ball from rolling down until you’re ready (we used a lego door).

Lego Erupting Volcano

I have to confess this one took a little bit of experimentation to get the mix correct before it worked well, but it got the most excited squeal of delight when it did!

This was attempt 2, too much bicarb inside, more vinegar needed! He loved adding it in!

What you’ll need:

  • A small tub or pot to act as the interior of the volcano and hold the mixture
  • White vinegar
  • Washing up liquid
  • Red food coloring (optional, but nice if you want red lava)
  • Bicarbonate of soda
  • An outside space or somewhere you can get messy

We built a volcano around half of an empty plastic bottle using both DUPLO and LEGO. Did you know that LEGO 4×2 bricks fit onto DUPLO bricks and you can mix them together? I didn’t, not until I did this….

Fill your container inside the volcano with a mix of 2 parts water, 1 part vinegar, 1 part washing up liquid and optionally a dash red food coloring. That’s your lava.

Get a tissue and make a bicarb bomb by wrapping several tablespoons of bicarb with the tissue and closing it up. Then you have a little pouch style package that will open at the top when dropped into the volcano. Make sure you rip off the excess tissue otherwise it will just bubble out of the top and spoil the effect. 

Give this pouch to your little one and bombs away, watch the eruption! Don’t expect anything too violent, it should ooze out nicely.

You’ll need to wash your lego afterwards (give it a bath or stick it in the dishwasher), and it might be worth trialling the mixture yourself to make sure it works and you’re happy before you do it for real.

What does this teach? Mixtures and mess can be a lot of fun.

Bridge Building Challenge

This one is more of a classic building challenge. I decided we needed to build a bridge that was both strong enough to hold a bottle of something (a plastic one! skinny syrup in this case) and also had room enough to drive a toy tank underneath it.

Easy he thought, but the first attempt wasn’t strong enough by far and the bridge bowed so much you couldn’t get the tank under. That’s when we learnt how to build struts and 2 levels of flat plates would make the bridge much stronger. 

A first attempt and a better way!

The final bridge was able to hold much more than one bottle too!

For this one you’ll need:

  • A bottle of milk or weight
  • A toy to drive under the bridge
  • LEGO! 

Marble Maze

Did you have one of those marble maze toys when you were little? You know the wooden box with the steel ball and the handles either side to tilt the maze? It took me years to be able to complete mine, and even then there was a lot of luck involved!

Somebody brought one into the office a while ago, and I was pleased to find it’s still just as hard now as it seemed back then.

A large lego baseplate is perfect for building a similar toy out of lego that you can just tilt with your hands. Start by building the finish line in the centre and build backwards to the edge (at least that’s what we did).

Make your own version of a classic toy!

This makes your toddler think about planning ahead, and making the path wide enough for the ball. They might need some help making a route that’s complex enough to be challenging. Helping with the route gives you the opportunity to explain about dead ends and trick paths, just like a real maze.

Frozen LEGO Figures

What I drew to explain temperatures…

The idea of this is to try to teach your little one the effects different temperatures have on things and to help them understand which rooms in your house are the hottest and coldest.

What you’ll need:

  • 3 LEGO Figures
  • A large ice cube tray, or ice lolly tray
  • Pen / paper
  • Thermometer
  • Timer

Unfortunately, it still won’t stop them from going outside in the freezing cold wearing a t-shirt. I’m not sure how you cure that.

Get 3 lego figures and encase them in ice. We happened to have a large frozen baby food cube tray handy that wasn’t being used for baby food any more. Lego men fit perfectly into this. 3 were chosen and frozen.

Tip: Lego men float, so I had to stick ours to a coin to sink them into the cube tray for freezing!

An Annabel Karmel baby food tray, great for freezing LEGO minifigures!

We then identified 3 rooms in the house using a little thermometer that had differing temperatures. The living room (normal), the boiler cupboard (warm) and the conservatory (coldest). We drew a scale and marked the rooms and their temps, then stuck the frozen lego men into these rooms and started a timer.

It was exciting to check every so often to see which one would escape first and educational to discuss what we thought would happen!

The hottest room in the house… would he escape first?

Marble Run

Make a marble run using LEGO. Towers of different heights with something for a mable to run down between them. This will probably be easier and quicker with DUPLO blocks, but if you have enough LEGO that will work too. Or use both!

As for something for the marble to run down, I’d suggest collecting used cardboard rolls from toilet or kitchen paper to use for this.

Fun to complete an achievement to get working and helps teach how to direct the path of the ball. 

LEGO Drop Test 

This is an experiment to help understand which shapes are the most resistant to impact. Give you little one a fixed number of pieces of lego, say 20. Then have them build something that when dropped from a height of 1.5m will survive the impact. 

What shapes do they build and which survives the drop? You can ask them to make a note of how many pieces broke away (if any).

This one didn’t survive the drop….

Stairway Building Challenge

LEGO stairway with spiderman on top
Spiderman probably doesn’t NEED a stairway, but this mattered little

Can your little one build a stairway that a LEGO figure can use to climb from one height to another? 

This will help test their understanding of how a staircase is held together.


Build a race track for 3 wind up cars, or 3 cars on a slope. Use some LEGO to create a starting pen that releases all 3 cars at the same time. If you don’t have any hinges or levers in your lego, just make 3 lanes and a lego barrier you can lift to set off the cars.

Sequence Puzzle

You know the sequence puzzles you get in children’s activity books? 

You know the ones…
What comes next?

Try making one of these out of LEGO blocks.The act of making the puzzle and knowing the answer from the start and having to get someone else to figure it out can spark a different emotional response to these puzzles, other than…. Oh that’s hard I don’t want to do it.

LEGO Tic-Tac-Toe

Make a tic-tac-toe (or noughts and crosses) game out of lego pieces. 

A LEGO Duplo tic-tac-toe board

Minifigure Board Game

Try making your own board game using a large LEGO baseplate. Maybe a maze with different colored squares, some traps, and a goal in the middle. Maybe find a dice. Make your own figures to play in the game. Encourage your child to make up the rules!

Lego battles are always a favorite in our house!

LEGO Teeter-Totter (SeeSaw)

Build a minifigure teeter totter using lego. Use it to demonstrate how different numbers of men and different seating positions along the beam have an effect on the outcome.  

LEGO Sweet-Box (With Lid)

Get your little one to make a box, with a working lid to contain sweets. The promise of sweets to actually put inside when completed should make this activity go more smoothly!

Other Useful Activity Resources

Here’s a list of 15 other fun STEM activities and science experiments from the STEM education guide.

Wondering about other ways to get your kids off screens? Here’s a useful list of 16 ways from the gamesguy.

If you’re looking for other things to do with DUPLO LEGO, think about trying some maths!

If you don’t want to use LEGO, or don’t have any Mytechclassroom also has a good guide to STEM kits you can buy for a preschooler or kindergarten child.


A stay at home dad and blogger. I'm lucky enough to have 2 wonderful children and the full set, a boy, and a girl! When I get a minute I like to share this tiring but amazing journey and my experience by writing!


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