Just in case this feature(s) should not even be unlockable for your own children who are part of Family Sharing:
Up to now, these children have been able to create their own playlists in Apple Music and share them as they wish. What could cause Apple to restrict collaboration between family members and patronize parents in this way?
That wouldn't fit in at all with the advertising on their website: 'Family Sharing. Share your favorite things with your favorite people. Family Sharing lets you and up to five other family members share access to amazing Apple services like Apple Music, ...'