That is so - though it depends on the actual chances; "much higher chance of survival" is different than "higher chance of survival".

But my point is that:

a) I might [currently thinking] rationally desire that all of my in-group would adopt such a belief mode - I would have higher chances of survival if those close to me prefer me to a random stranger. And "belief-sets that we want our neighbors to have" are correlated with what we define as "good".

b) As far as I understand, homo sapiens do generally actually have such an attitude - evolutionary psychology research and actual observations when mothers/caretakers have had to choose kids in fires/etc.

c) Duty may be a relevant factor/emotion. Even if the values were perfectly identical (say, the kids involved would be twins of a third party), if one was entrusted to me or I had casually accepted to watch him, I'd be strongly compelled to save that one first, even if the chances of survival would (to an extent) suggest otherwise. And for my own kids, naturally, I have a duty to take care of them unlike 99.999% other kids - even if I wouldn't love them, I'd still have that duty.