The only genetic difference between male and female babies is that males have 1 X and 1 Y and females have 2 X's. If there is a survival difference that is genetically based (and I don't know if that's true), then the lack of a second X chromosome might explain it.
just gonna take a guess... the X may possibly aid the child in how long they live. and the Y would too but not as much. this makes sense because a guy is XY and more die at birth and don't live as long as a girl which has XX