[zozbot234]

Kids have very little agency to begin with, so looking out for #1 is a fully rational strategy from their POV. As an adult, you grow a lot more comfortable with your situation and it becomes natural to "expand the circle of concern" beyond oneself.

[cucumber3732842]

I think it has more to do with agency than age except that agency increases with age.

Look at prisoners, people dependent upon disability, people in authoritarian societies, you see all the same stuff. They're just more tactful about it because they're adults.