Cut out large egg shapes on heavy weight paper, help them stick strips of painter's tape or masking tape across it. Then they paint the paper - with brush, fingerpaint, whatever. After it is dry remove the tape, revealing the white that was covered by the tape. It will look like a decorated easter egg. Could also add stickers and stuff afterwards too. I can see this doable for a wide range of ages.

this website has the same idea, except they used wet chalk:

http://www.momto2poshlildivas.com/20...aster-egg.html