Actually, it's ever so slightly higher than 1/2 because there is a non-zero chance of them being identical twins. If we assume an identical twin incidence rate

Actually, it's ever so slightly higher than 1/2 because there is a non-zero chance of them being identical twins. If we assume an identical twin incidence rate of 0.4%, then the actual probability would be 63/125 that the second child is also a girl.