Marshmallow Structures STEM challenge - with a Valentine twist!

Have you tried the marshmallow challenge? You are going to want to try this marshmallow challenge with a Valentine twist straight away! The good news is that you don't need many supplies. This marshmallow STEM challenge is lots of fun and perfect for budding engineers. Using just straws and marshmallows kids are challenged to build a 3D marshmallow structures in the shape of a heart!

Marshmallow Structures STEM challenge - with a Valentine twist!




What is STEM?

Since I have used the word STEM in the title I want to start with a quick definition of STEM for anybody that is new to STEM activities.

STEM stands for Science, Technology, Engineering and Maths. By combining these subjects children can learn how to be creative, develop thinking skills, problem solve and evaluate. Science, Technology, Engineering and Maths are everywhere in the world around us and by providing fun hands on activities we can encourage our little ones to develop a healthy interest in these important subjects.

Hands on projects like this heart themed marshmallow challenge are a great way of encouraging young children to develop problem solving, design and building skills. As they get into this fun engineering project they may also need to experiment and modify their structure as they see what does and doesn't work.

This STEM challenge is a great activity to do individually, but it is also great to do as part of a team where ideas can be shared and kids can work together to complete their structure.


More Valentine STEM projects:






marshmallow STEM challenge


The heart themed Valentine twist to this marshmallow challenge makes it perfect to do during Valentine week, but it's fun for anytime of the year really! We have used heart shaped marshmallows but plain marshmallows work just as well (or even balls of playdough.)

As well as taking on the build a 3D heart challenge you may want to give our marshmallow snowflake challenge a try. The snowflake challenge uses marshmallows and toothpicks to build structures. Another fun engineering activity is to use spaghetti and marshmallows and see who can build the tallest tower!

Don't waste any left over marshmallows, use them to make marshmallow slime (or eat them!)


Marshmallow Structures Valentine STEM challenge


marshmallow structures


Marshmallow structures supplies:


  • 16 heart-shaped or large plain marshmallows
  • 8 paper straws, cut in half
  • 3 additional straws, cut in thirds (You will need 8 pieces)
  • Scissors, for cutting the straws in half

For the optional additional challenge:

  • Additional straws and marshmallows

The marshmallow challenge


Marshmallow STEM Challenge  - BUILD A 3D HEART!



Valentine STEM challenge - build a 3D heart from marshmallows and straws


STEP 1: Prepare supplies


Setting up this STEM challenge is super easy. You just need to cut the paper straws according to the sizes in the supplies list and then set them out on the table alongside the heart shaped marshmallows.

cut straws for building structure

STEP 2: Challenge children to build a 3D heart


Once you have set up your supplies instruct the children to build a 3-dimensional heart using the marshmallows and straws.

If the children struggle to construct the heart, mention that it is easier to build one heart first by connecting the longer (half-cut) straws into the marshmallows, using the marshmallows as a joint between straws. The straws may need to be twisted while being pushed into the marshmallows to make them stick.

Use straws to build a heart design

marshmallow heart structure

Then, push the shorter straws (third-cut) vertically into each marshmallow. This creates the supports for the second layer.

3D marshmallow heart structures

Children should continue building the second layer by pushing marshmallows onto each vertical straw and then connecting the marshmallows with horizontal straws.

building a heart marshmallow stem challenge

3d heart marshmallow structures

Some children will find this challenge easy, others will need support and suggestions. Looking at the images above will help some children with making their 3d heart.

Valentine marshmallow 3D heart activity for kids

Extra optional challenges:


  1. Once the hearts are built, challenge the children to make the structures more stable. If multiple children are each constructing their own heart, test to see who has the strongest heart by picking them up or by placing paper on top one sheet at a time.
  2. Challenge the children to create a smaller or larger heart using the same methods.


Valentine marshmallow STEM challenge - Make 3D heart marshmallow structures.

We hope that you have fun with the kids trying this marshmallow STEM challenge. You could even try making other marshmallow structures!


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