Strasburg is probably your best choice for a family outing. If I'm not mistaken, there are outlet malls not too far away (the latest in Amish fashions at discount prices and fantastic deals on buggy whips!

), and the Railroad Museum of Pennsylvania is almost right across the street. Not sure if it's still there, but there was also a pretty decent car museum nearby. Any of these attractions could take at least the better part of your day, although not all may interest all members of your family. While I've seen the remnants of Steamtown when it was in Vermont, and its beginnings in Scranton, I've not yet visited there. My good friend cn nutbar highly recommends it though, and most of the operating locos are either ex-CNR or ex-CPR, as is one of Strasburg's.
My favourite train attraction in Pennsylvania, though, especially when the trains are not running, is the East Broad Top: this place is a time capsule and, at least for me, very nostalgic of a whole way of life that's slipping away. Not a bad place for the whole family when the trains are running: there's a short out and back ride in vintage coaches. When the trains aren't running, it's a lot easier to have a look around. The last time that I was there, a few years ago, was a week before their annual fall double or triple header weekend. I fell into conversation with a guy working near the turntable, who was obviously in charge of the area. As he had work to do, he suggested that I go take a look in the roundhouse; more or less "enjoy yourself, and don't get hurt". None of the locos were in steam, and it was too dark for photos, but wow! The sights, the smells, climb into the cab and have a look around, let your imagination run back 50 or 70 years, and just soak it in.
Wayne