The National Christmas Museum!!!
It's hard to describe and I love, love, love it. The museum is an outgrowth of one man's love of the holiday and it explores all kinds of aspects of the it. The first time I went I was expecting something a wee bit cheesy and silly, which it kind of is, but it's also so much more. I CANNOT stand in the "Woolworth's" without getting a little weepy, seeing all the old-fashioned decorations I remember from my great-grandmother's house. The train exhibit is so fun and there's a collection of creches at the end that show how the Holy Family is interpreted around the world in various media.
I can't recommend it enough.
ETA: If either of your girls are budding engineers or scientists, you might look into "Rough & Tumble" - a museum of steam power. It's more fun than it sounds, I promise! My husband (an engineer) and son totally geek out, but my daughter (whose 7) likes it, too. Many of the exhibits are outdoors and I don't know the winter operating hours, but if it sounds up your alley definitely check it out.
Also, if you have any lingering American Girl enthusiasm (or doll love in general), there's a store nearby Lancaster that has tons of clothes and accessories for 18" dolls, plus lots of items for Madame Alexander and other high-end dolls. The store is called Aimee and Daria's Doll Outlet (dolloutlet.com) and is in Ronks, right on Route 30.