Turn off family sharing for child

Here is what to do If you forgot your Apple ID password - Apple Support — you may (will?) need to contact Apple Support directly to resolve this password reset, if what’s listed in that Apple article doesn’t allow regaining access.

Without the direct assistance of Apple Support, children under 13 can only be transferred to another Family Sharing. There’s no provision for removing and releasing a child under 13 from Family Sharing.

Note: The child’s age for this is typically 13, but the age can vary by country or region.

Could you elaborate? Your Apple ID and email, and that of your child and their Apple ID and email, are separate, and can be added or removed separately.