As for catching the fish, I don't get to fish Pymie as much as I would like, but have had success every time that I went. It is one of the better crappie lakes that I have ever fished, and you should get into some fish. I do have success with crappie a bit south of there. I like using 1/16 or 1/32 jig heads (either sickle hooks or I widen the gaps myself). Either minnows hooked through the lips or Gulp minnow (1" or 2.5"). I also tie up my own jigs that often out fish either, always good to have minnows though. Under a bobber (I like the foam with lead bottom), try different depths. I usually start about 2' down, and adjust if no bites, ect. Often, I am catching fish with the minnow/jig less than a foot under the bobber. Try leaving still for a few minutes, if nothing try slow retrieve, jigging it a few times (even with minnow works great) and letting sit. Avoid letting it sit for 15-20 minutes with no bites. Stop at an area, try to fish as much of that area as you can, if no bites within 1/2 hour, move. Try the stumps, hit 5-6 different stumps, if no catching, go closer to the shore line and look for old weed growth. Fish on top of the old growth, cast around until you can find any. They might be on their spawning beds, which would be away from the stumps themselves, but nearby. If fishing is really slow, take the bobbers off and troll really slow with the minnows until you find some fish (lots of snags in the stump area, so do this with care). Crappie will tend to stick together, so try to cast right where you caught the last fish. Often, you can catch 5-10 fish in one spot, cast 2-3 feet away and not get a bite... If absolutely no bites, try going a bit deeper. Find a point on the lake, go 30-40 feet out from it, and drift by it with your minnows just above the bottom (let line out until it hits bottom and take a wind or two of the reel). If that all fails, try bluegill fishing, or just cruise around in the boat!!! Kids love just cruising. Not sure about the 14 year old, might not be enough action for him, but if one of the first times on a boat, I'm sure he would be fine with it. Explore some of the islands, ect. If it has a steering console, you are golden. Able to let them steer, they will love it. Tiller is a bit more complex, and you could end up going for a swim if they accidentally turn too hard... I'm sure your 14 year old would be fine, but might turn into an issue that one was able to drive, while the other wasn't.
Don't be scared to ask around at the bait shop of what is biting and where. Most of the time they will lead you in the right direction. They want repeat business.
If looking to buy a boat with kids in mind, I would strongly suggest something with a console that you can stand up and walk around a little on. 16'-18' or bigger if getting a pontoon. Nothing like stretching your legs or standing while fishing and not feeling like the boat is going to tip. Kids can get up and check out one seat to the other. If fishing is slow, they can do other stuff and not be as confined, or they can steer the boat while cruising like mentioned. I used to take a toy box with me, with crafts and other toys for the kids. Minnows are hours of entertainment for kids as noted. If you put the effort of driving to a lake and launching a boat, you don't want to be out on the lake for an hour or two, unless you are in a dock/slip and easy. When fishing from shore, if fishing is slow, you can go to a playground or other form of entertainment pretty easily. Not really the case on a boat.