Some comparators
Child #1 - Passport photo taken at 28 days old. Valid for 5 years for both US and SA.
Child #2 - Passport photo taken at 14 days old. Valid for 5 years for both US and SA.
At about 2-3 years old, we got them both Global Entry. At enrollment, the Officer who rolled their prints was not confident that, at the GE kiosk, our (e.g. me and kids' mom) use livescan pad would work to get a good match. Never had a problem. Have also had to lift them up off ground to get a camera view of them on the GE kiosk. Made for some interested "half-photos" that the CBP staff often chuckled at us for at least making the effort.
US
Under 16 get passport that only lasts five years
https://travel.state.gov/content/tra.../under-16.html
16 years and older get passport valid for ten years
https://travel.state.gov/content/tra...ort/16-17.html