Let’s face it: a lot of people may have created Apple IDs for their kids for convenience while skirting Apple’s rules about the age at which an account can be created. That’s 13 in the U.S. and many countries, unless you use the option within Apple’s Family Sharing to create a Child Account.
If you weren’t using Family Sharing, however, and—ahem—invented an earlier birthdate for one or more child, you can still rewind the clock and gain the advantages for age-based control within Family Sharing.
For our family, that includes not just using Screen Time to limit and monitor access to all their Apple devices, but—and the kids actually like this—remotely disabling Screen Time if they are on a sleepover or away on a school trip and we are willing to let them use their screens past our household limits. (That was a selling point to at least one kid, along with access to a much larger pool of shared iCloud storage.)