Love, love, love Lancaster, PA for very young children. Dutch Wonderland has a lot of fun rides for the entire family, that are fun for preschoolers. There's also visiting an Amish farm, Sight and Sound theatre productions--all very family-oriented. There's also great shopping and food for the adults in the family. Never been to Sesame Place, also in PA, but heard it's great for preschoolers. And, Hershey Park looked very attractive, but I missed out on the discounted rates. If you're looking for later in the year, you might have better luck, but the Hershey Lodge looked fabulous. These are all within driving distance of the greater Washington metropolitan area. I didn't see where you lived, but have you thought about being a tourist in Washington, DC, which is always a treat for all ages. There's Six Flags in Largo, MD, the Smithsonian museums on the mall (Free Admission), the National Zoo, Rock Creek Park, etc., and stay at the National Harbor in Ft. Washington which is breathtaking, and offers so much to do and see. You could even take a boat ride over to Alexandria and take a walking tour of Old Town Alexandria.