Change child birthdate
How do you change a child’s date of birth under the family account?
Note the restriction if you entered a date that made them less than 13 years old.
Apple ID - Update the birth date associated with
If necessary, contact Apple ID Support.
Apple Support by e-mail or chat Work through the screens to get a chat option.
Or fill out and submit this form. The form is for iTunes, but it will get passed to the ID Support section.