If the phone is associated with a child’s Microsoft account, and their account is part of a family, adults in the family will be able to see reports of their child’s online activity, find their child on a map, and help make sure their child doesn't see inappropriate websites, apps, or games.
If you already added your child to a family, and they've signed in with a Microsoft account, you're done!
If not, first, add your child to a family by going to account.microsoft.com/family and selecting Sign in > Add. Then have them sign in to their phone with their Microsoft account. If they don’t have one, select Create an account instead of Sign in, then follow the instructions.