Marshmallows and toothpicks are one of the most accessible 3D engineering materials available. The marshmallows act as flexible joints that hold toothpicks together at any angle, allowing children to build genuine 3D geometric structures — cubes, pyramids, triangular prisms — that would be impossible with flat paper crafts. The material set is cheap, edible (the marshmallows), and requires zero tools beyond fingers. It's a compelling engineering activity that simultaneously teaches geometry in a genuinely tactile, spatial way.

What You'll Need

• Mini marshmallows (larger ones work but mini are easier for small joints)
• Round toothpicks (flat toothpicks are harder to push in)
• Gumdrops or jelly beans as alternative connectors
• A flat work surface

Start with 2D Shapes, Then Build to 3D

Stage 1: Flat Shapes (Ages 3–4)

Build flat 2D shapes on the table: triangle (3 marshmallows, 3 toothpicks), square (4+4), pentagon (5+5), hexagon (6+6). Count the sides. Observe which shapes feel rigid and which wiggle — a triangle is rigid; a square can be pushed into a parallelogram.

Stage 2: 3D Shapes (Ages 4–5)

• Cube: Build a square base (4 marshmallows, 4 toothpicks). Add 4 vertical toothpicks pointing up. Connect the tops with 4 more toothpicks and 4 marshmallows. Count: 8 vertices, 12 edges, 6 faces.
• Triangular prism: Two triangle faces connected by three rectangular faces.
• Pyramid: Square base with 4 toothpicks rising to meet at a single top marshmallow.
• Icosahedron: For older, patient builders — 20 triangular faces.

Stage 3: Engineering Challenges (Ages 5+)

• Build the tallest freestanding structure.
• Build a structure that holds a book on top.
• Build a structure using only 20 toothpicks and 10 marshmallows.
• Build a bridge between two cups using only marshmallows and toothpicks.

Frequently Asked Questions

Are toothpicks safe for preschoolers?

Toothpicks have sharp points and should be used with direct supervision for children under 5. For younger children (3–4), use craft sticks cut into thirds as a safer alternative to toothpicks, or use blunt-ended cocktail skewers (available at kitchen stores). Some schools substitute dry spaghetti noodles for toothpicks — they're blunt, break easily if poked, and create the same engineering challenge.

What is the strongest 3D shape that can be built with marshmallows and toothpicks?

The triangle is the fundamental rigid shape — any structure built from triangulated faces (like the tetrahedron or the icosahedron) will be significantly stronger than one built from square faces (like a cube). This is why triangles appear throughout engineering: in roof trusses, bridge structures, radio towers, and geodesic domes. Challenge children to see whether adding diagonal toothpicks to a wobbly cube face makes it more rigid — it will, instantly.

Can you use other materials instead of marshmallows?

Many alternatives work as connectors: gumdrops, grapes, clay balls, playdough balls, cheese cubes, or foam balls. Each material teaches something different — grapes are juicy and connect differently; clay can be molded to specific joint angles; foam balls can hold more toothpicks per joint. The variation in materials is itself a learning exercise in material properties and engineering constraints.

Related STEM activities: Straw Tower Competition | Build a Bridge | Pipe Cleaner Engineering