One of the best parts of Family Sharing in iOS 8 is that you can closely monitor your children's purchases, even when they're not with you. Even better yet, you can create an Apple ID just for them that once they're old enough, they can take with them. But until that time, it can help you keep a watchful eye on content and purchases on any iPhone or iPad they're using.
How to create a new Apple ID for your child for use with Family Sharing
Note that you'll need to create ID's for children in your house from a device that belongs to the Family Organizer.
Launch the Settings app on the iPhone or iPad of the Family Organizer.
Tap on iCloud.
Tap on Family.
Tap on Create an Apple ID for a child — it's all the way at the bottom in small writing.
Enter your child's birthday and tap Next.
Agree to the terms and conditions presented.
Verify the credit card you have on file by entering your 3-digit security code and tapping Next.
Enter your child's name and tap Next.
Create an iCloud ID and tap Next — remember this is the ID your child will use forever, so make it something they'll be ok with when they're old enough.
Read the warning that pops up and confirm that's the ID you want by tapping Create.
Choose a password for your child's Apple ID.
Create security questions for your child's Apple ID — they can always change these along with their password when they are older and you release the ID to them.
Choose whether or not you'd like Ask To Buy to be enabled and tap Next.
Choose whether or not you'd like the child's location shared with other's in the family group — for most folks, this answer is probably yes.
Agree to the terms and conditions.
That's it! Once you're done, you can allow your child to start using their new Apple ID on any iPhone or iPad they have. Anytime they try and make a purchase, you should be asked to confirm it, as long as you chose to enable the Ask to Buy feature. Once they're 13 or older, you can decide to let them manage their own ID going forward, if you'd like. Otherwise they can remain on your Family Sharing account with Ask to Buy enabled until they are 18. At that time, you can remain as a family but the Ask to Buy option will no longer be available as they are considered an adult at that point.