Apple would prefer if you didn't share one AppleID, even for children. Anymore that is like sharing a social security number.
Family sharing + restrictions is a safe way for a child to have an iPhone without the security risk involved of them having access to your AppleID (even restricted). By default if the child is under the age of 13 all purchases will need to be authorized through you, if they are over 13 you can still enable that feature.
Sharing an AppleID also limits functionality for those with multiple devices since Apple would need to develop around the idea that you AppleID, iCloud, and email can only be sync'd in very specific ways.
Also there are other limitations like iCloud space, maximum number of iCloud devices on one account, etc.
I would give Family Sharing a try, and if you don't trust your child or over protective or whatever (not trying to be offensive there just lack of better term) let them know you'll randomly be checking their device and if you see something you don't like then you'll remove that function from them (ie messages, safari, app store, etc).
