One of them is a boy (but we don't know which one).
With two children there are 4 a priori possibilities (in order):
BB-BG-GB-GG, each with an equal chance of 14
The GG must be left out, because we know that one child is a boy.
There are two chances with a girl (BG and GB) out of a total of three leftover possibilities, so the chances are 23
Hope this helps!
