My mom taught 1st grade and under for years. She gave me this playdough recipe. According to her, it will last for a very long time if kept tightly wrapped. She said she only replaced it when it got grungy from 30 little hands playing with it.
3 C Flour
1-1/2 C Salt
6 t Cream of Tartar
Heat to near boiling:
3 C Water
3 T Cooking Oil
Dump liquidd into dry mixture and stir fast and hard with wooden spoon. Knead when cool.
Add food coloring and knead into the dough. Store wrapped tightly in airtight bag.