How to delete a child's account

Hello selfm73,

Please refer to this support page to learn how to delete an Apple ID - How to delete your Apple ID account - Apple Support

If you need to update the age of the child's account, please refer to https://support.apple.com/en-us/HT204164.

Please note deleting an Apple ID will remove all data associated with that Apple ID and the data will be lost unless it's backed up / saved somewhere else.

I hope this helps!