E is married to A or D. But B is married to D. Thus, E is married to A. Thus, A, B, D, E are the four adults and C, F, G are the three children in the family.
B and D have a child G.
A and E have two children. They are C and F.
Now, only F and G are girls. So, C is a boy.
Thus, C is A's or E's son.