What do I do if my child is too young to sign his or her passport book?
A parent or legal guardian may sign the passport if the child is too young
to sign his or her own name. To do so, a parent or legal guardian must print
the child’s name and sign his or her own name in the space provided for
the signature. The parent or legal guardian must also write his or her
relationship to the child in parenthesis next to the signature (e.g., parent
or legal guardian) so we know who signed for the child. http://travel.state.gov/content/passports/english/passports/FAQ
