How to use Family Sharing on iPhone 4 and other devices?
I turned on Family Sharing for my kids on my iPhone 5 that has iOS 8. After entering their emails, I entered their passwords. On their iOS 8 iPads, purchases from all the family members show up, but not on the iPod 4 or iPhone 4.

However, my kids on those devices still have "Ask to buy" show up. If you want them to have access to all of your apps, you could jailbreak (redsn0w for iPod 4 on iOS 6 and evasi0n for iPhone 4 on iOS 7) and install Account Changer. If it weren't for the "Ask to buy," we would have stayed with Account Changer only.