Combine 2 tblsp self-raising flour and 2 tblsp salt in a small bowl.
Add enough water to make a smooth, thin paste (consistency like yoghurt).
Divide into separate bowls and add a drop of food colouring to each.
Get the kids to use thin paintbrushes on thin cardboard. Apply quite thickly for best results.
Place their completed artwork in the microwave for 30 seconds and watch it puff. Take care removing from microwave.