We went there two summers ago, and my dd (then 4) had a blast!! The "trail" or pathway around the largest room/cave was pretty long, but worth every step. (Bring a water bottle!) It was nice and cool temp-wise down there, but I do suggest bringing a light sweater to tie around your waist - just in case - especially if you are bringing along little ones. I believe the temp stays around 56 degrees year round.
I also suggest callling ahead before you go though, because I heard (I think last year) that they either were
thinking of or
would be closing the caves to the public!!

Something about some water dripping into the caves or something? Not sure, but I remember thinking, "Man, I'm glad we already got to go experiance that!!"
Oh, and I would stay overnight in town, if you plan to stay. But that's just my opinion. I believe there's only one motel and restaurant out by the caverns, and I was hesitant to stay or eat at either place. White's City is about 7 miles from the caves, which you have to pass through to get to the caves, and then there's Carlsbad - which is about 20 miles from White's City. I can't remember how large a town White's City was, but you could look that up if you're interested.
Also, be sure to ask (if you call ahead) if and when they will be doing the "Bat Flight". This is where you can watch bats fly out of the caves at dusk, during the summer months. We didn't stay for that, but I hear it's really cool to watch.
The drive out to the caves is some of the prettiest scenery I've seen in New Mexico. Just be carefull and watch the road, though. There are some steep drop offs, and winding areas of the road.
But if you are able to go this summer, I would definately go. You just never really do know how long natural wonders, such as Carlsbad, will even be an option to you. Hope you all have a wonderful time!! And be sure to come back and let us all know how your trip went!!
Here's a link to the FAQs at the National Park Service's website on Carlsbad:
Carlsbad Caverns National Park - Frequently Asked Questions (U.S. National Park Service)
I found it helpful when I researched going there.
HTH!!