DS and I went to Lancaster county PA to see the train museums (yes there is more than one all close together) in Strasburg. when he was 2yo. We live about 10 minutes west of the George Washington bridge, and it only took us about 2-3 hours to get there (longer on the way back b/c I took a wrong turn towards Philly at rush hour.)
We stayed at the Bird-in-hand Family Inn, in Bird-in-Hand PA (yes that is the name of the town.) It was a really nice place to stay, but everything closed on sunday. It had playgrounds, pools, minigolf and so forth right there at the hotel. It looked like a lot of places in the area have similar facilities for families.