Make sure you check the possibility of getting the Passport Card (less expensive), but make sure it will work for all your future travel needs.
As is looks right now, after June 1, children under 16 can still use their birth certificate. See below.
"CHILDREN: U.S. citizen children under the age of 16 will be able to present the original or copy of their birth certificate, or other proof of U.S. citizenship such as a naturalization certificate or citizenship card."
If in doubt regarding children under 16 it might be best to call for verification.
