re: Fun things to do in Houston

Kemah Boardwalk (tourist trap but still fun for the kids)
Pleasure Pier in Galveston
Houston Zoo
Downtown aquarium
Memorial City Mall play area for the kid
Children's Museum
Bayou Wildlife Park in Alvin
Depending on when they are coming, a Skeeters or Astros Game
The Rodeo (shite ton of fun stuff for kids and adults during the day)
Space Center Houston

Come on, there is a ton to do in the Houston metro area.