I forgot my childs apple id account. Can I retrieve it somehow?
How do I retrieve my childs apple id and password?
See if you can recover the ID/password. Use every email address you can think of.
Apple ID - How to find your Apple An iCloud e-mail address is an Apple ID.
If you forgot the Apple ID password, enter the Apple (iCloud) ID, and click Forgot Password. See if you can get an email option if necessary.