Ages of Sons

Problem

There are two guys standing before a building with multiple floors.
First: "I have three children, the product of their ages is 36, can you guess their ages?"
Second: "No"
First: "The sum of their ages is equal to the number of floors in the opposite building, can you guess now?"
Second: "No"
First: "My youngest son is a very good dancer"
Second: "Yeah, I know now"
Assuming that both these guys are extremely intelligent and follow common-sense logic to find out the ages of first's children.