I lived in OKC for almost 5 years and there is so much to do. Here is a link that might help...especially since the ages are widespread.
http://okc.about.com/od/attractionsa...thingstodo.htm
Also, T-Shirts are always a hit. You might even want to help them make a t-shirt for you or your DH with their hand prints on them...my DH loves the two he has. Then you write their names and ages near their prints.
I just know whatever is chosen...you will all have fun and take away great memories :) :) ENJOY!!!