My son just turned 7. I mailed my documents a few days ago.
When I sent the pack it had my cover letter, application (spousal) with extra photo, passport, birth certificate, then a cover letter for my son, being submitted under me (primary applicant), with his Application, birth certificate, passport and custody papers, plus a travel letter that shows his father authorizes travel (just in case), then I tabbed all of the supporting documents and included behind the applications.
We will see in a few days if that is acceptable ;P
Laura