1 cup liquid tempera paint
1/4 cup liquid laundry starch
2-3 Tbsp liquid dishwashing or laundry detergent

Dilute with water to your satisfaction.

Mix thoroughtly before painting.  You will be amazed at how quickly pictures dry when children use this mixture.  It really cuts down on the drippies and pictures are dry enough to put in backpacks in just a few minutes.