My effort includes giving each kid a paper plate, opening the bags of marshmallows and giving each kid some toothpicks. Remembering to buy the marshmallows is probably the most challenging aspect of the craft.
The kids attach the toothpicks to the marshmallows to make structures.
This is my contribution.
As you can see, you can do much cooler things than cubes.
This was originally two different structures.
I would suggest starting with small marshmallows and plain toothpicks. When they seem in danger of getting bored with the craft, then you can start buying marshmallows of different sizes and toothpicks of different colors.
Also, the marshmallows can double as a snack in a pinch. The only issue is storing the finished projects, which I've solved by sticking a few in a display case and taking photos of the rest.