Use Screen Time with your family
If you're already in a family group, go to Settings > Screen Time, and tap your child's name. If you need to create an Apple ID for your child, go to Settings > [your name] > Family Sharing > Screen Time.
Or if you're new to Family Sharing, tap Set up Screen Time for Family and follow the instructions to add a child and set up your family. You can add family members any time from Family Sharing settings.
To use Screen Time with Family Sharing, you need to be the family organizer or parent/guardian in your family group, on iOS 12. Your child must be under age 18, in your family group with their own Apple ID, and on iOS 12.
https://support.apple.com/en-us/HT208982
Use parental controls on your child's iPhone, iPad, and iPod touch ...
https://support.apple.com/en-us/HT201304