I know when it happened, but I'm not quite sure how. We had been watching the British series "Upstairs Downstairs," and I guess started singing "What are we going to do with Uncle Arthur," but of course changed to "What are we going to do with Baby Charlie." And the next thing we knew, Charlie was singing along.
Every night. Like clockwork.
Well, now we've finished "Upstairs Downstairs." And "The Forsyte Saga." And "I Claudius." And "The Duchess of Duke Street." And now we're on "The Jewel in the Crown." So the songs change, but one thing remains the same. At the end of each episode, Charlie still demands we sing.