How about an indoor water park. They have various locations around the US.
http://www.greatwolf.com/grandmound/waterpark
Also, try a cruise. I went when my son was 2 and he loved it. They are rather economical because all of the food is included. My Son was too young for the on board kid activities(aka babysitting) but your kids ages should be OK.
If you are still considering Disney do a combo- Disney cruise and Disney.
Be safe and have fun!
P.S. Some cruise lines offer discounts for members of the military.