They don't want to be found, vastly preferring life in the outdoors over being cooped in school all day.
So many prime children!
I would guess there was none. A plane doesn't stock up on people by age.
It could also be that they died in the crash like the adults did.. I prefer the former.
I think GP was making a joke implying those were numeric identifiers for the children rather than their age, and that the identifiers had to be sequential.