I found this great idea in the Gymboree Play and Learn Book.
Take 4 packet unflavored gelatin
2 cups cold fruit juice, apple or grape- no pulp
2 cups hot fruit juice, heated until just boiling
The parent part: Pour the cold juice into a large heatproof bowl. Sprinkle the gelatin over the cold juice and let stand for 1 minute. Add the hot juice and stir gently but thoroughly until the gelatin dissolves. Pour into an ungreased 9x13-inch cake pan and refrigerate until set.
The toddler or parent part: Use cookie cutters (simple shapes work best for small hand) to cut out the jellies. Or a parent could just cut them into squares.
The toddler part: Poke the jellies with your finger. Stack them up and watch them shimmy. Bounce them. Oh and eat them too!