Hello, thank you for reaching out to Microsoft Q&A.
Only the Organizer of your Family group can edit the Child's personal info.
May I please know if you've already added the Child account to the family group? Are you unable to manage consent from an organizer (Adult) account?
This is what worked for other users:
- Create a new Adult account (Dummy one) or use another adult account of yours.
- Invite the Child account to the family safety group - https://account.microsoft.com/family/home
- You should see the child account in your adult account family group, where you can manage consent for them and edit the personal info.
On the next screen, you've these options to edit the D.O.B for the child account.
If you're having issues, you can remove the Child account from that group and use another account of yours and see if you can edit the child's personal info from that account.