I just made playdough for String Bean and friends. It is pretty easy:
2 cups of flour
1/2 cup of salt
1/2 cup of water and then some
Mix the flour, salt and 1/2 cup of water together. You will need more water. Add water a small amount at a time until it makes a dough-like consistency. You probably want to use a spoon first and then your hands (take your rings off first!) to get it mixed well. Add food coloring. You will get it all over your hands, so be careful not to wear your favorite, most expensive white shirt when you do this. It washed off my hands pretty easily, not to worry.
It is edible, but not suggested for those on a low-sodium diet.
I read in a magazine that you can add essential oils to give an aroma to homemade playdough. I'm not that girly. Not that there is anything wrong with that. But it won't be edible any longer.
I have mine in old baby food jars. Using the Gerber stage 2 size jars, it should fill about 6 jars. I didn't have 6, so I put my extra in snack-sized ziplocs.
I did notice that the playdough tended to dry out the more I handled it, so you may want to have a small cup of water available for when your kids are playing with the playdough. Of course a smock wouldn't hurt either so they don't get flour and food coloring all over their clothing.
...Maybe you should just go purchase playdough after all.