This past Saturday, my wife and I took our 2 yr 11month old newphew to the museum. None of us had been there before. We had a great time! Not only was it a Saturday, it was the busiest day of the year - Spring Break Saturday. Although the ticket line was long, we had no problem with any other crowds. The museum is large enough and laid out well enough that huge crowds were not a problem.
I highly recommend this to anyone with children!