Such a good idea as a gift for grandparents. Put a phrase or message in vinyl letters on a clean canvas. Have your child paint a picture on top, then peel the vinyl letters off to reveal the message underneath.
I remember making salt dough ornaments as a kid. This method, using baking soda and cornstarch looks interesting: Dries quicker, smoother and whiter than traditional salt-dough Cups Water 2 Cups Baking Soda 1 Cup Cornstarch