Code #1- is mainly used for security check.
Code #2- Biometrics (Photo, one Print and signature )it is used for finger print on your GC
Code #3 - code 1+ code 2
If you only take code 1, USCIS may consider you cann't get GC in a short time.
code 2 or code 3 are must to get card.
Children are not required for security check. They take code 2 FP only.