Childs age
The birthdate is wrong on my child’s Apple ID, is there a way to change it without deleting the Apple ID and creating a new one?
Read this support article about how to update the birth date associated with an Apple ID: Update the birth date associated with your Apple ID - Apple Support
There's different ways to change the age on an account depending upon the age of the person, their target age, and the country's age definition of "child".