Where I live there is an indoor aquarium relatively nearby. The plaster gallery is fun (depending on age though). Also, depending on where you live, indoor waterparks are great. You can go to a shopping mall and have a contest – give each person/team a list of things to find/take a picture of and meet back at a certain time to compare findings.
I don’t know about what’s in the Poconos now, but we went a long time ago for a couple of days and it was a great vacation.