The family connection.
Children from 4 families are playing together. A guest asks me how many children are in each family. Being the low life I am, I say that my family is the largest, my brother's family is smaller, my sister's is smaller still, and my cousin's is smallest of all. I also divulge that there are fewer than 18 children and that the product of the numbers of children in the four families is the same as my house number (which the guest knew). The guest thinks and then asks me if my cousin's family consisted of a single child. I say no. You now have all the information you need to tell me how many children are in each family?