I've been there and can give some first-hand information:
First, it IS difficult to find. They may've given you the impression on TV that it's a big-deal place, but it isn't. It's really just a little place up a dirt road. In the spring/summer months it gets crowded, and parking's difficult so people just park on the side of the road.
Right now is the WRONG time of year to even think about this activity. Wait 'til nice weather in spring. Children will get WET, so you don't want them out in the cold. You want them to have fun so they'll want to do this again! Also, don't let them wear anything white or any good clothes; they WILL get dirty, and they MAY ruin clothing. Here in this area, we have red clay, and it stains.
When you get there, you'll buy buckets of dirt -- they'll be lined up waiting for you, and you can see the backhoe with which they dig up the dirt. It's been 2-3 years, and I can't remember for sure, but I think they had cheap-o $5 buckets and "higher quality" $10 buckets.
You take your buckets to a "trough" through which water runs, and there are screens that you use to sift through the dirt. If your boys are young, you should probably just get dirt for them, and you supervise. It's really easy, and you'll definitely find stuff, though it probably won't be valuable. It'd be wise to bring a jar to tote home the new-found stones. Two children will probably fill a medium-sized peanut butter jar with 1-2 buckets of dirt each. Expect a bucket of dirt to take 30-45 minutes to "sift". Just buy them one bucket each to start with, and if they're still having fun you can go back for more.
You'd be also be wise to bring along a couple soaking wet wash cloths or hand towels in a ziplock bag -- forget baby wipes, they aren't going to clean this kind of dirt! Experienced moms leave the ziplock bags lying on the hood of the car in the sun so they'll be nice and warm for kid-cleaning (this is a family kind of place, and no one'll steal your stuff). If you plan to go to eat, etc. afterward, you should bring clean clothes to change into.
The only food available at Hiddenite itself is a drink machine. Okay, that's not food. There are picnic tables up in the woods, if you bring your own goodies.
There's a small "store" -- think shed turned store -- that sells inexpensive stones turned into necklaces, etc. My girls always admired these, but they wanted to make things themselves from THEIR OWN stones. We bought them a rock polisher (that's not the right name) and bought some cheap stuff at AC Moore's, and they had all sorts of nice necklaces.