I bought the Crayola finger paints and they are very nice, but when I run out of those I mix a bit of flour, small amounts of water added at a time until you get a good texture and add food colouring. You can make cornstarch mix the same way. I make sure they use the fingerpainting shiny paper with this really wet paint so they don't rub through the paper. I like to do things the simplest way possible.

Oh mimi, thanks for that, haha! My dckids drive me crazy that I put all the colours out and it all ends up one big colour.