The crayon method: Take your eggs hot from the boiling water (adults do this, cuz they are HOT) and then let the kids put wax shavings from crayons or use sharpened crayons to decorate the eggs. The wax melts and creates really fun rainbow designs. And if you're 3, you practically create your own egg-shaped crayon because watching the shavings melt is so much fun
On the left are the eggs done with a Volcanic Paint technique - baking Soda painted onto the egg then vinegar food coloring added. All the kids loved this technique, too.