You don't have kids, do you? Small kids don't really understand money. When a parent downloads a "free" game, they expect it to be free. When their kid starts crying because they can't do anything without buying something in app, it pisses the parent off. Or, once burned, you have this scenario:

"Can I have this game, daddy? It says free!"

"No, honey, it costs money".

"But then why does it say free?"

"Because they're telling lies to you to try to get you to buy it."

You can't really avoid that conversation.

If you want to charge me for a kid's app - PLEASE do it up front. I've spent more money buying my kids apps than I have buying myself apps. It's not the money - it's the deception that game makers try to push on my small children. I can do without that.

*edit - the first sentence reads a lot snarkier than I intended. I should have left that out.