All the six members of a family A, B, C, D, E and F are travelling together. B is the son of C but C is not the mother of B, A and C are a married couple. E is the brother of C. D is the daughter of A. F is the brother of B. How many children does A have ?

Answer: C. Three

B is the son of C but C is not the mother of B means C is the father of B. A is married to C means A is the mother of B. F is brother of B means F is son of A and C. D is daughter of A means D is daughter A and C.

A has son B, son F and daughter D  i.e., three children.