[Joe Ross]

I think it comes down to, how are the kids selected to answer the door. I don't beleive the problem is clear enough, and that's why you have two different arguments for the answer.

When Kris reads the problem, he sees no method for picking which kid goes, and so assume random. That throws out the possibility of 2 boys, and also 1 of the 1 boy 1 girl possibilities. You get 1/2

When Denman and FizMan read the problem, they see that if a girl is in the family, she is sent out first. Thus, you can only eliminate the 2 boys possibility, and get 1/3.

Is one or the other the correct reading? Make your arguments to convince me.