Don't know what their interests are, but here are a couple of ideas on each side of the spectrum:
Blanchard Springs Caverns I've been in quite a few caves and this one is special because it is pristine. It was protected from early on and is in great shape. Nice picnic area with cool river to play/wade in during warmer months.
Crystal Bridges Art Museum I'm generally not one who visits art museums, but the art here is of amazing quality and almost entirely from the U.S. from since before there was a U.S. One important thing to note is that it is FREE!
If you end up on I-40 through OK, an interesting campground is
Red Rock Canyon SP just outside Hinton, OK. FHU. Pool in the summer. In a canyon in the plains, You don't know it's there until you drop in. Nice place to play for the GC's.
Depending on where you are going in NW NM might determine how to get back to Denver. If your route can take you through Salida, CO, spend a few days there. There are ghost towns to visit, great scenery, fishing, and white water rafting for everyone from novices to the very experienced. Our teenage nieces live in the mountains of CO and Salida is the favorite place that we take them. The town itself has developed a nice restaurant row, interesting art shops, and one can wade or float on tubes right through town.
