My wife and I recently took our 2.5 year old daughter to the National Gallery in Washington, DC. As we walked up to the building our girl asked if this was the museum and then shocked us by stating that she wanted to see the ballerinas. It took a minute but then we realized that her Olivia book [listed in the "Things We Like" sidebar, of course! — Ed.] has a picture of Degas' ballerinas and a Jackson Pollock. The National Gallery has both sculptures and paintings of the dancers by Degas.
We took our little one to see the sculpture first and by the time we headed upstairs she already had enough. The hack: my wife started playing the "I spy with my little brown eye" game. It worked like a charm. The artwork gives you plenty to "spy" and our girl really got into the game. We only stayed about an hour but it made the visit much more enjoyable for us and everyone else at the museum.