If the lifeguards look out for the safety of all guests in the swimming pools, I see no reason not to allow pool toys, including balls. My dd and I purchase a new ball on each trip - the smaller ones which usually have the year printed on them. We have fun playing toss, and we've met so many other kids who want to play with us.
I'm disabled and can't move around a lot when I'm in the pool. This can get a little boring for my dd, who's not old enough to be too far away from me. A ball provides a little extra fun. We find a spot in the water that's not crowded and we don't throw it far or hard (we toss rather than "throw"). If it's really crowded the ball stays in the backpack.
I have witnessed people of all ages who throw balls and use other pool toys in an unsafe manner. Every guest has the right to feel safe in the pool. If the lifeguards do not react, it should be called to their attention. I'd probably talk to the guests myself and respectfully request that they find a safer location to play. Usually, when you use a friendly, positive approach with people, the response is positive, too, especially at WDW!
PS- If you're really nice and have a friendly smile on your face, it makes it much harder for the other person/s to ignore your request, including a lifeguard!!!
