The Strong Museum is really unique and one of the best museums for children.  They will love the Seseme Street section and all of the hands on areas.  Margaret Woodbury Strong had an extensive collection of toys and dolls.  Not only can you see many of these, they have it set up so that kids can play with some.  They have a play house, a play Wegman's grocery store, a train, sand box and many other areas with fun for all aged children.  They are currently adding on an indoor butterfly area.  Check out their web-site www.strongmuseum.org/ .