The Apartment Number Wasn't Enough

A piano tuner chats with a client about her three children. "The product of their ages is $36$," she says, "and the sum of their ages equals my apartment number." The tuner glances at the number on the door, thinks, and says: "That's still not enough information." The client adds: "My oldest child just started violin lessons." The tuner immediately names all three ages. What are they?