1/2 cup corn flour
1cup wheat flour
1/2 cup salt
2 tbsp oil
1tsp cream of tartar
11/2 cups water
Mix all together over medium heat in a pot till it's lump free, a thick play dough consistency and the salt is dissolved. 2-5 minutes.
Divide ball into individual portions and colour to your hearts desire.
Adjust dough with more flour or more water till you have a soft, smooth consistency.
Let your kid mix the colours. Don't have dumb authoritarian rules about what they can and can't do. Have fun. Make worms and smarties and balls.