Directly from the State Department website:

https://travel.state.gov/content/travel/en/passports/need-passport/under-16.html

Children Under 16

All children under age 16 must apply for a passport in person with two parents or guardians using Form DS-11. You cannot renew your child's passport using Form DS-82. Passports for children under age 16 are only valid for 5 years.

Wow. As a passport acceptance agent, I can tell you, the children are required every time. Children's passports aren't renewed. You need every thing, every time. Without the child there, how do we know it's the correct child? Children change appearances very quickly, that's why their passports are only good for 5 years. You could literally provide a photo of ANY child and claim it was the same one.