I had a problem similar to this with a fire effect on my player.
I'm not sure if this help, and I'm a bit of a noob, but...
I would try making the prefab that has the balls bouncing around it, actually create the balls as objects / spawn them in.
Then spawn that object in.
That's the best I could tell you without more info, it would be helpful if you provided more information about your problem.
As in how are the balls moving? Are you using the mecanim animator / legacy animations, are they controlled by fsm's?