I don't know how much longer they will be doing this, but we went a few weeks ago and since my husband is active military, we all 4 got in for free (2 adults and 2 kids). They are doing a thing called "Here's To the Heroes". Adults need to have ID to get in free.
Edit: Just found a link. http://www.herosalute.com/
Edit: Just found a link. http://www.herosalute.com/