The complication is that the app is designed for children, while the customers are parents. How do parents feel about opening a browser vs. an embedded view of web content? I can’t find any best practices.
Some apps I have seen add some kind of heavy handed “gotcha” type test to filter out younger users, but the experience is sub-optimal and kids are generally smart enough to subvert most of these types of controls anyway. What I decided to do, at least until I can gain some feedback from future tests, is to simply hand off to safari with the belief that if access to the web is a concern to parents that they will have set up controls on the phone, or at least monitor their children’s usage.