Wall mounted ball run. This would be great for kids who are too young for the marble runs. Could be used as a music installation if there are movable obstructions in the pipe that make sound when a ball touches them
Recycled Toilet Roll Ball Drop Game with Ping Pong Balls! Great for toddlers and preschoolers! We totally did something like this in China for C only instead of ping pong balls we used food pouch tops.
Another pinner says: Mess Free Finger Painting! What an awesome idea! Paint in a ziploc bag taped over a piece of paper. Of course we'll have to REALLY finger paint sometimes, too, since getting messy is half the fun.