Mix the bicarbonate of soda (baking soda) and corn flour together.
Add in the warm water a little at a time until you have it the consitency that you want. If you want a really bright colour then it is best to leave the consistency thicker and adjust once you have added the colour.
Divide up the mixture into small bowls.
Add a few drops of food colouring to each.
Mix well with a spoon.
Pour your mix into the squeezy bottles. Shake well.