Hello
The short of it is that Minecraft is a building game. It's digital Legos. As far as skeletons, zombies, and the area that could basically be considered "hell" by some, the objective if to fight the things typically. If the children are spending several hours a day on it, that's a parenting problem, not a Minecraft problem. If the children's morals are somehow at risk because of the previously mentioned elements in the game, that is again a parenting problem. Now, I'm not saying let them play anything and everything, my argument is simply related to Minecraft. There very much exists games and other forms of entertainment that I'll go as far as saying even adults need to question why they participate in it.
When I was a teenager I actually brought my Dungeons & Dragons books to church to show them to my pastor. He'd heard about it, but never had anything to do with it because he was raised in a time when that was a no-no. After looking it over he said, "so this is basically just a template to be creative." We played a few times at church. How did we play? We made our characters (yes, including the magic characters) and we were the good guys the defeated the bandits and goblins and restored the town... typical good guy fantasy stuff. Why didn't they have a problem with the magic at church you may ask? Because we were sitting around crafting spells and other such questionable behavior. We simply said, "my character does this" and rolled a couple of dice for the results. Does that mean other people didn't do things with the game that were absolutely uncalled for, disgusting, and highly questionable? No, because they did.
Likewise, Minecraft and other such games allow creative freedom. What I would be more concerned about is observing what the children do with that freedom.
I also want to point out that the 14 y/o is at a point in life where he/she (I don't remember if they are boys or girls, sorry) will be facing considerably more insidious and destructive things in their life than Minecraft will ever remotely dare to be. I am not saying to accept something small because there are worse things, I just want to make sure things are in perspective. I decided to take a good look around a while back when I started questioning some of the video games I play and shows I watch. "Bad" is everywhere. Unless you keep the tv on the Hallmark channel and only read Christian books (which can even be questionable at times), you and them will be exposed to the secular world. Honestly, I'd be hard pressed to find something more neutral than Minecraft.
Another question... skeletons, zombies, and hell are bad and children shouldn't be exposed to them is what some believe, right? Do you allow those same children to read their Bible? Do we hide them away from Hell, demons, leviathans, behemoths, murder, sex, incestuous sex, and a whole host of other things we could go on about? OR, do we sit down with our children and guide them, raising them up in the way that they should go?
Communication has to be open with the children. Ask them how what they do helps their relationship with Christ. Ask them also how it could potentially harm their relationship with Christ, or their witness. Don't lead them to answer the way you want them to answer either, let them answer openly. THEN, guide them in the direction you think is best according to Scripture.
All that said, my personal opinion is this: Grades are down and Minecraft is being played 4 hours a day. That's not Minecraft's fault. That's the fault of nobody saying, "Since you cannot play video games and do your school work, you cannot play video games Sunday through Thursday. And you will not be playing all day on Friday and Saturday." It's not some kind of evil insidious game corrupting the children like a digital Ouija board from a horror movie. It's a weakness in boundaries and guidance that is actually somewhat easy to fix. As far as the children not sounding "normal" because they talk about a game they enjoy and mention *gasp* dragons... at 14 count your blessings that's all you're hearing being discussed lol.
Just guide them and love them, and I'm sure this will work out.
Sorry for the long post.