Stayed at the Carlsbad RV park - KOA was just too remote. CRVP needed some updating of the power poles and that work was well underway last August. Large, level sites, just a short way from town and much closer to the cavern
After doing the cave, check out the public "beach" in Carlsbad! Neat little City park along the river. Surprisingly nice for a walk or picnic or whatever one does in a park.
Try to go to the Cavern entrance at least an hour before sunset to watch the bats leave the cave. Amazing experience! Quiet except for the sound of the bats, no cameras clicking, very little talking. Hundreds of thousands of bats each night. There were no kids around in late August so can't comment.
The Ranger led tour into the special, normally closed areas of the cavern was well worth it. The Great Room is amazing but the closed areas have some very delicate formations and the Ranger talk is very educational. -- including a short 'lights out' period