Family sharing
As the family organizer , if someone would buy something would it automatically buy it or ask approval first?
iPhone 6s, iOS 9.3.1
Only for members under the age of 18:
Turn on Ask to Buy
The family organizer can turn on Ask to Buy for any family member who isn't an adult. It's on by default for any children under 13, and you'll be asked if you want to enable Ask to Buy when inviting anyone under 18 to your family group.*
Use these steps to turn Ask to Buy on or off for family members who are under 18* in your family group. If you turn off Ask to Buy for a family member after they turn 18,* you can't turn it on again.
Here's a link to the complete article:
Request and make purchases with Ask to Buy - Apple Support
Cheers,
GB