Traci's ideas sound great!
You could also try pairing up with with punny sentiments (computer generated is a good way to go here!) or even jokes for kids' cards. Things like "you have me in a spin" or "what's a tornado's favorite game?" (put the answer inside the card - Twister!).
Could you make a fun abstract-looking background with it? Use funky colours and turn it at different angles on the paper, maybe? Or in interlocking rows if the angle of the point works OK for that.
Can you show us an image of the stamp to see if that sparks any other ideas for us?