What is the probability that all of the children in a family of five children will be boys?

The genders of children within the same family are not independent. So the answer will depends on the pattern of children's gender in the family's ancestry, as well as the age of the parents.

However, if you make the unreasonable and unjustified assumption that the genders are independent and that the probability of either gender is 1/2, then the answer is (1/2)5 = 1/32.