Marshmallow geometry is a fun way to teach the names and characteristics of 2D shapes including triangles, rectangles and squares. Kids love having the chance to build 2D shapes with food and grown ups love watching children practice important math skills. It’s a winwin!
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Getting Ready
To prep, I gathered together a few simple supplies:

 Pretzel sticks (toothpicks are easier to build with so grab them if you have some on hand)
 Mini marshmallows
 Card stock (or construction paper)
 Marker
I quickly drew four 2D shapes on a sheet of card stock and labeled each one (equilateral triangle, isosceles triangle, square and rectangle).
Since my daughter’s knowledge of geometry at this point consists of basic shape names, I wanted to help her look more closely at shapes to notice how they are built; how many sides and vertices they have, whether they have parallel lines or perpendicular ones, and how long their sides are. That’s why I decided to start with the simplest 2D shapes she could build: the triangle, square and rectangle. I labeled each one with its name then left a spaces for A to write out how many sides and vertices each one had. Then, I called a very eager A over the play.
Marshmallow Geometry
“Can you tell me the name of these shapes?” I asked as I pointed to each one.
“Triangle, triangle, square, rectangle,” A easily replied.
“Yes! And can you point to and count the sides of this triangle?” I asked pointing to the first triangle. My daughter quickly counted three. Next, I explained that the spot where 2 sides meet to make a corner is called a vertex. I showed her how to label the vertices with a red dot and helped her label the vertices on the rest of the shapes.
“Ok, here is a bowl of vertices,” I explained, handing her the bowl of marshmallows. “And here is a bowl of sides,” I continued, passing her the pretzels. I demonstrated how she could build the shapes using the marshmallows and pretzels.
A couldn’t wait to start building and even though the pretzels were a little tricky to manipulate, she kept at it. I had toothpicks on hand just in case the thicker pretzels were too troublesome, but A didn’t want to swap them.
“Can I eat it now?” she asked as soon as she finished building her first triangle. She was pretty disappointed when I said, “No.” I placed the triangle on top of the one I’d drawn with marker and asked her to count the sides and vertices again. Then, she wrote the totals on the blank lines.
We moved on to the next shape. “Another triangle?!” A said confused.
“Look closely at the two triangles. Are they the same or different?” I asked.
When A replied they were the same I had her use a pretzel to measure each of the sides. She noticed the second triangle had longer sides but the top triangle had sides that were the same.
“Yes, this one has equal sides and is called an equilateral triangle,” I explained. “The other has two sides that are the same and one shorter side. That one is called an isosceles triangle.”
These were new terms for A and I was not expecting her to memorize them – I just wanted her to notice that not all triangles are the same.
“How should we build the isosceles triangle if it has 2 long sides and 1 short one?” I asked A. She thought for a moment, then bit off a piece of pretzel and proceeded to build the isosceles triangle.
We continued counting sides and vertices and building more 2D shapes. When we got to the square and rectangle, we talked again about side lengths.
“What is the difference between a square and a rectangle?” I asked A.
“A rectangle is bigger than a square,” A said after a moment of thinking.
I grabbed a piece of chalk and drew a square house with a rectangle door on it and a rectangle skyscraper with small square windows. I asked her in each picture which was bigger – the square or the rectangle? After realizing her mistake, A again used a pretzel stick to measure the sides of the square and rectangle.
“The rectangle is LONGER!” A shouted when she discovered the difference. I gave her a high five and she was thrilled she came up with this discovery on her own. While building the rectangle A made it lean to one side. She laughed at the wonky rectangle.
“That is actually a different shape called a parallelogram.” I said. Maybe it was the sugar from the broken marshmallows she had been eating, but she thought that was the funniest word she’d ever heard. Eventually after the giggles died down, I explained that a parallelogram had two sets of parallel lines. Then I explained what parallel and perpendicular lines are.
“Can you point to the perpendicular lines in this square?” I asked, reminding her that perpendicular meant crossing by making my fingers into a cross. Then, she pointed to and counted the pairs of parallel lines.
When we had finished talking about the four 2D shapes, I let A build whatever shapes and structures she wanted with the left over materials. Later that day, I had A set the dinner table asking her to place the fork and knives parallel to each other for the kids and perpendicular for the adults. I’m pleased to report that she’s got the new terms down!
Want More?
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