JH and I visited the Legoland Discovery Center at the Plymouth Meeting Mall.
There's a "mini" Legoland at the Plymouth Meeting Mall. It's not like the big park in California, it's more of a playground and activity center. There's a little four-seater train car to take you into the center, complete with a laser pointer shooting game that JH absolutely loved. Some of the other highlights for us were the activity center where you attempt to make a Lego tower that can withstand an earthquake, and a Ninjago-themed laser maze (we did that six or seven times I think).
There was a great recreation of the major Philadelphia landmarks, like Geno's (and Pat's) cheesesteaks, the Liberty Bell, City Hall, Penn's Landing, and Reading Terminal Market.