What I'd really worry about is what happens when some backdoor captures and sends your child most frequent location to someone else? (now imagine that someone else as a network of pedophiles or organ traders)
This is an iPhone app, I think it could be solved by using a specialized separate device (not connected to any other computer (including the Internet)).
Well I would think most people wouldn't be comfortable with any company having record of their kids locations all day, every day for years [1]. Why would any sane parent want to give away this data to a startup?
Parents who buy this app are crazy(imo).
[1]sure your cell phone service provide has this data but (a) that can't be helped (b) location tracking isn't their business and (c) they don't specifically target kids).
I mean from a marketing standpoint you can sell it, and sell lots of it, but if you educate your users by saying that "by installing this app you increase the risk that bad people locate your children more easily, and then possibly kidnap them", I would doubt they'll buy it.