Cornstarch and conditioner with a few googly eyes. Adding equal parts to begin with adding more cornstarch or conditioner until a dough like consistency is reached.
I would suggest an apron for this activity if the little ones are more on the messy side. It is also a good time to remind them not to touch there face when they are cooking or working with other substances such as the cornstarch.
The finished product, plus a piece of a leaf because the little one wanted her frog dough to have a green tongue.