Solve my probability doubt?

Question

A parent gives birth to two children. One of the child is surely a male, what is the probability of having both male child?

Common answer 1/2 Actual answer 1/3

Answer 1

There are two children, so the distribution of gender can be $(M,M),(M,F),(F,M),(F,F)$. The case $(F,F)$ is excluded. This leaves you with the situation

$(M,M),(M,F),(F,M)$

So the probability of two males is $1/3$.

Answer 2

There are 2 children. Which child is surely a male? Think about it for a while till you get it.