Kay, find / buy one of those high bounce rubber balls - we used to call the super balls when I was a kid. I think you can buy a package of them at the dollar stores. They are often in with the party favors, as small gifts / prizes for children. I'm talking about small ones, about an inch diameter. Large enough it can't be swallowed, small enough for the following:

Leave one in the tub. Sparkle LOVED to go in and have a hockey game! Of course, she enjoyed doing this at 2 AM as much as at 10 AM.

George is the right age, you may have to swat it around once or twice to give him the idea, then he will have his own game going! I used to just leave it, it settles on the drain, so I didn't worry about me stepping on it and falling. Thus it was available whenever she wanted to play with it!