Hello Robb471, Welcome to the Community. WE understand you are needing to update your daughter's birthdate.
When going to Settings, selecting the Samsung account and then Family, the only option available are to remove or add members. You may need to remove your daughter and then re-add her with the updated information.
You can also reach out to the Samsung Accounts team to see if they have any other options available. They may be reached by calling 1-855-795-0509.
