Birthdate Change for child

Only a Family Organizer can change the birthday of a child, and the child must be associated with the family group.

Which means forming a family group if one does not already exist, the child joining the group, and then changing the date.

Update the birth date associated with your Apple ID - Apple Support

Family Sharing - Apple

See Update the birth date associated with your Apple ID - Apple Support

Okay. Maybe some confusion. We’re not Apple Support. We’re other users.

If you’ve set up the family sharing and the child has joined, and if the organizer is not getting the change message or some other issue is arising, then I’d try logging out of iCloud on both the child and the family organizer’s devices, rebooting both, logging into the respective Apple IDs on each, and trying the birthdate change again. Failing that, yes, contact the folks at Apple Support.

Use Get Support, and you’ll probably want to look for the Chat option if that’s available.

When I get into my daughter's apple ID and try to change her birthday (from adult to child), it says the family organizer must make the change. I'm the organizer. I get the email from Apple saying "click Approve Request", but there's nowhere in the email to click on. Where do I find "approve request"?

Contact the folks at Apple Support, then. Adult to child is... unusual.