Thank you everyone. I have actually been to the south rim and would prefer it, but the granddaughters really want to do the skywalk and the trip is really for them. Totally agree it is a tourist trap and too expensive.
Grapevine Canyon does look interesting and I hadn't read anything about it previously. I'm also leaning towards taking a detour to visit the Grand Canyon Caverns, I think the kids would like that.
Should we do the Caverns and back to Kingsman to spend the night or on to Seligam and stay there?
Thanks again for all the pointers, it's hard to know when you're not familiar with the area!