New Mexico: Carlsbad Caverns National Park
If your kids love Batman, then you must come to Carlsbad Caverns National Park about 150 miles east of El Paso. The huge caves are a draw in themselves, descending into a seemingly bottomless pit in the ground. The evening bat exodus, however, is just incredible.
If you come to Carlsbad, you'll have your choice of two self-guided tours. The Red Tour uses the elevator going both up and down, and the scope of your tour will be limited to the Big Room. It's true to it's name -- as it's big enough to hold the Capitol Building and is as long as 14 football fields. If you and your kids are in good shape (and are not claustrophobic), skip it and go straight for the Blue Tour. This will take you through all of the cave open to the public. The kids will love descending down the 91 stories along the paved switchbacks. It's two miles of walking though, so make sure you're not going to have to carry anyone!
At dusk during the summer months, the bats will explode out of the cave and darken the sky. A ranger provides narration, and your kids will be awe-struck. For more information on Carlsbad, you can call (505) 785-2232 or visit them on the web