Ah, it's no big deal! I put mine in the pile of toys in the kids room. It was there each time I came into the game until I decided to click on it. For some reason that made it disappear, and I haven't seen it again. Lol! I'm done looking for that illusive red ball! Would be different if the kids could play with it. It looks like Christian is playing with it here, but he really isn't:

Remember where you left the ball, then go to the other slots and click in the same place. For example, I put it in with the kids' toys, so when I clicked on the toys in the other games, it appeared there as well.