Due to a ping pong ball battle of my son (1 1/2) with his cousin (3) came to get a pool balls the idea. The reviews for the Pop Up Pool convinced and the pool was charged with 500 balls ordered separately. The shipping was fast, the stuff well packed and I can join some reviewers: Nothing smells like plastic. After establishing my son sat happy as punch in the pool and paddled, dipped, fondled the balls and looked perfectly happy. This is now permanently so with intermediate throw orgies.
Conclusion: Ingenious acquisition, we do not like to miss. The pool is well sized for a child. 500-600 balls should be minimum. We ordered another 300 more so that it is really funny. The balls hold of some, but are nevertheless so that a child can not do anything if it falls.