First of all whip up a batch of basic cake mixture and divide between six bowls.
250g caster sugar
250g self raising flour
drop of vanilla (or flavoring of your choice)
Beat together the butter and caster sugar. Add the eggs, milk, and vanilla. Sieve the flour into the mixture and stir.
Add a few drops of red, yellow, and blue food dye to the first three bowls. This is also a good chance to talk about primary colours.
Then use the remaining three bowls to mix the colours together to make a green, orange and purple mixture.
Using a different spoon for each different colour put a blob of mixture into a cupcake case, layering the colours on top of each other.
Pop them in a preheated oven at 180 degrees and cook for about 10-15 minutes.