If you're a Bank of America cardholder (debit or credit), this weekend is free museum weekend. There are over 150 participating museums across the US. Find one in your area at museums.bankofamerica.com.
I think we'll be taking M to the Please Touch Museum in Philly and the Garden State Discovery Museum in Cherry Hill this weekend. She's never been to the Please Touch Museum, but she loved the Discovery Museum when we went in January.