Family sharing
How do prevent sharing adult books with children in family sharing?
iPad Air, iOS 8.2
You might want to consider this ..
Kids under 13 can have an account, too.
Now kids under 13 can have their own Apple IDs. As a parent or legal guardian, the family organizer can create an Apple ID for a child and add the child to the family group automatically. Ask to Buy is turned on by default, and the organizer can also limit the content kids have access to on their devices through Restrictions on an iOS device or parental controls in OS X and iTunes.