I put in the wrong age for my child. How do I change it?

If that is an error message you are getting, you will need to contact them.

Apple ID Support

Apple ID Support (2) 

Apple Support by e-mail or chat    Work through the screens to get a chat option.  You may need to pick a problem that is slightly different than yours to get a chat option.  

Apple Support using Twitter

Or fill out and submit this form.          The form is for iTunes, but it will get passed to the ID Support section.  

Note the under 13 restriction.

Apple ID - Update the birth date associated with