Regarding "nag their parents" -- be careful, be very careful, you are treading on sore thumbs here. If my preschooler starts nagging me about IAP prompted by whatever ad mechanism that is in the game, the app gets promptly deleted and it gets 1 star rating and a review with a warning to other parents.

As I said in another comment, while I do not like to say "no" to my kid, I really hate him being used as a pressure point for milking parents for IAP money. If your app is respectful towards the parents, I will gladly pay you and probably more than you think.