There are many families with two children, both male, or both female.

So...

Does the sex of the first child affect the probability of the sex of the second child?

I.E.

If the first child is a girl, is it more or less likely, or just the same that the second will also be a girl.

Likewise, if the first child is a boy, is it more or less likely, or just the same that the second child would also be a boy.

If the sexes of the children were truly randomly distributed, one would expect for 2 child families:

M M

M F

F M

F F

Thus, giving half of the families with one boy and one girl, and a quarter with two boys, and a quarter with two girls, or half having two of the same sex.