Here's the recipe I've always used - the cooked method.
Add to saucepan:
1 cup white plain flour
1/2 cup salt
1 cup cold water
2 tsp cream of tartar
1 tablespoon oil
food colouring of your choice
*I also added some strawberry essence to the pink and peppermint essence to the green
Cook on med-high heat and stir stir stir until it begins to bind together.
Keep stirring till it's all in one big clump. That's it you're done.
When the kids have had enough you can be store this in an airtight container in the fridge for a couple of months.