I’m not talking about teens so much as the 5-10 year old range here, but you can totally play Dungeons and Dragons with your younger kids. We’ve started games in the last couple years with our boys who were both in elementary school at the time so the following are observations we’ve made during games with them. YMMV.
Reading level and Math
While adding dice scores is easy for most kids, the concepts of armor ratings and attack bonuses might not. When an attack calls for you to pause the game to sit down and tally up dice rolls with weapon proficiency or whatever else, you might lose the focus of younger players. Just as well, the details of things like spells and abilities might be lost on them if they can’t comprehend the text. This is also an excellent opportunity to teach counting higher numbers and focusing on reading paragraphs.
Content and Emotional Matruity
Not everything in DnD is age appropriate for 5-10 year olds, and that’s fine. Just don’t use it. Does your pre-made module call for big busted succubi or demon lords? Change it to something that won’t give your first graders nightmares. That’s the beauty of DnD, you can just swap out monsters or make up new ones and just use the stats from the ones in the monster manual. Let your kids fight a pizza monster that just happens to have the stats of a beholder. Maybe the room full of burning skeleton knights can be a room full of slime knights. It really depends on the maturity of your kids, if they get scared by stuff in kids movies you’ll want to modify the mobs.
This is probably the biggest hurdle you’ll run into playing games with your kids. Here’s what will happen, one kid will begin their turn by moving towards a spider mob. While that kid is busy rolling dice and reading through their abilities the other kids at the table will become restless and bored. This often results in them playing with dice, dropping them on the floor, drawing on their character sheets, not paying attention to the combat or being disruptive to the rest of the game. It’s not their fault, they’re just kids, but this is another reason to simplify both combat and character stats. Do you really need +1 modifiers to weapons? Do they have to roll half a dozen d6? Do they have to take penalties if they’re on rocky ground? Do you really need to roll for initiative? Not kidding, just pick for them, it will save time and make things run smoother.
So if your kids already play videogames they’ll be used to the concept of multiple lives, attempts, and resurrection. If they die they can just start over from the beginning of the room. In DnD your character can totally die and be dead forever. I don’t suggest giving them magic reviving items or do-overs, but go over the options of sneaking past monsters or solving puzzles to get through rooms as opposed to running into a room swords swinging. Guide them through it if you have to. Never get frustrated with kids if they run into trouble with a mob or get upset if a roll goes bad. You might have to hop out of the DM seat and assist them, it’s ok.
Roleplaying with kids
So even after you’ve come up with simplified options for classes, races, and alignments your kids might just go on with their own concepts for their characters, and that’s fine. Just be aware that sometimes the barbarian might want to try casting magic missiles or the paladin will rather search for treasure than help villagers being attacked by goblins. Just go with it, the whole point is to let them have fun. You can slowly increase the difficulty and implement the true rules as they get older and understand them better.
Terrain and Minis
Remember the part about attention span? Having something physical to show your kid where their character is on the map can be a huge help with combat and puzzle rooms. Take your kid to your local comic or game store and let them pick out a figure, paint it, name it, make it theirs. If that’s not an option, let them pick out a toy form their toy box, small action figures, amiibo’s, etc work just fine. Batman can fight kobolds just as easy as anyone else. Speaking of kids toys, get out the legos, the toy castles, etc for terrain. You don’t have to use your expensive custom painted multi-level tavern model for the kids.
Breaks and when to end the story
With adults and teens you can pause and get up from the table when your turn isn’t going on without much issue. Depending on how long your kids can keep up with a campaign you might not be able to get very far. Give them chances to get up and walk around, get a snack, go to the bathroom etc. This won’t be a 5 hour marathon like it is with your buddies from college, you might make it two hours total. MIGHT. Keep the combat short and important. Needless battles with seven layers of 1/1 creatures better be pushing that story hard. Let them fight the boss, start them off at lvl 5. Make it fun, don’t play DM mind games with them. Perhaps the whole campaign is just recovering an item from a cave. When they start to nod off or begin wandering away from the table to do something else, wrap it up and pick it up again the next weekend.