We will be driving from Philadelphia to Boston in one day with 4 kids. Any suggestions on short stops along the way? Traffic getting through NY?
To avoid traffic in New York City, just don't go through NYC. If you avoided I-95 and the NJ turnpike, you can go from Philadelphia up US1 around Trenton (New Jersey) and then up US 202 to I-287 - this takes you across the Hudson at Tarrytown on the Tappen Zee Bridge. Tarrytown (near Sleepy Hollow) would be a nice stop-there's a Riverwalk Park and a Lighthouse. Continue on I-287 N. Take CT-15 N, I-91 N, I-84 E and I-90 E through Hartford (Mark Twain House) and Worcester Old Sturbridge Village (although this may take more time than you want to spend.
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Newport would be a nice stop. You could pick one of the mansions to visit like Marble House or The Breakers. Also enjoy some great seafood at a local restaurant like Benjamin's.
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Mystic Aquarium in Mystic is fantastic!