Because all children are different, and because, in the area of RPGs, a child's age is not as important, I've come up with KID levels. KID stands for Kids Interactive Development.
The KID levels are:
Level 1: Pre-Verbal KID: Child can't speak, or doesn't speak clearly yet. Roleplaying opportunities are limited to pre-verbal communication: physical movement and "adult as jungle gym" style play, baby signs, early forms of costume play, and the dreadful pre-verbal horror LARP "Gotchernose."
Level 2: Pre-Literate KID: Child can't read, or reads only with a lot of assistance. Roleplaying opportunities are limited to oral tradition game rules, freeform LARPs
(Cops & Robbers, etc.), and very simple roleplaying in board games/card games/ etc. Costume & prop play is also viable.
Level 3: Early Literate KID: Child can read, but does not read well independently (doesn't read on their own, reads only for schooling, etc.) This is the first KID level where playing tabletop RPGs become viable. Freeform LARPs and some LARPs with rules (Rock, Paper, Scissors) become viable, as well. Card games like Pokemon & Magic: The Gathering become viable, which can lead to roleplaying content.
Level 4: Free Reader KID: Child can read and does often on their own. Child is capable of creating a basic personality and some small amount of history & background for their characters. LARPs with rules are definitely an option.
Level 5: Advanced KID: Child is capable of picking up a brand new RPG book, reading it, and rolling up a character without much assistance. Child is capable of creating a character's history and background, and a fully-realized, well-balanced personality for their character. Optionally, a child referee (Game Master) may be able to run their own scenarios at least moderately well.
Level 6: Expert KID: Child is capable of running a regular game and keeping other kids interested. Child is capable of picking up a brand new game, reading it, and figuring out how to generate characters without assistance. Complex LARPs become viable. It's also very possible for a child of this level to actively participate in games with adults without causing problems. Essentially, a child of this KID level would basically be a fully-grown gamer.
Level 7: Accomplished KID: This KID level is for children who are able to do all the things in the Expert level, plus they actively work to get other children involved in gaming. Perhaps they run a regular game themselves, and they also are capable of running a LARP.
Obviously, KID levels don't necessarily correspond to a specific age, but I do feel that mental and emotional maturity does have something to do with it.
So, in order to run a game for kids:
1.) Establish the minimum KID level for a game you wish to run. Of course, the higher up the scale you go, the harder it will be to find children who fit that KID level.
2.) Decide what game you're gonna play. I've had great luck with d20 games, FUDGE seems simple but interesting, and other people swear by GURPS, and there's plenty of other games that kids *could* conceivably play.
3.) Decide who you're gonna play with. Some people come equipped with potential kid gamers. Others have to find them. Here's some ideas for those of you who'd like to try this, but don't have any children in your immediate family:
* Scout group
* Church group
* School group (particularly, I've found, the Gifted & Talented programs)
* Children of friends who are gamers
* Local area science fiction & fantasy groups and conventions
* Children of members of your friendly neighborhood SCA
What's important here is how you go about this - you don't want to seem like Mr. Smelly in a Rubber Raincoat. You need to come across as Joe or Jane Helpful, who is interested in furthering the cause of kids and gaming. Make the situation fit the context in which you're looking.
4.) Decide where you're gonna play. The "where" question is the most important one, because that can make or break a game. Obviously, many game stores have areas where people can play. If your game store doesn't, then why not ask if you could run a game in the store? That might bring in business and it will certainly be cool for the kids. Some libraries have publically available conference rooms that they'll let you have for "Free or cheap." Many of the larger chain bookstores have cafes that you could conceivably game in...in fact, one of my very first D&D games with kids in my adult life started in a Borders' bookstore cafe - once I started playing, I definitely attracted a lot of other kids to the game just by playing. Kids would come up out of the blue and want to play! Amazing, huh? But it would happen. If you do happen to use your church youth group or some other contact with a church, be sure that the youth leaders don't have a problem with role-playing as a hobby.
5.) Whatever you do, make *certain* you get parental consent before you game with a kid. Even if you know the parent personally, you should talk to them before you get their kid involved. There are a lot of people out there who are still stuck on the whole "Gaming is Evil" concept and you never know when you'll run into them. It's better to be safe than sorry!
6.) Decide when you're going to play and for how long. Basically, a good rule of thumb is that games take about 6 hours, four hours of which are actual play and the rest is filler: social discourse, bathroom breaks, snack breaks, meta-discussions, and bickering. The best way to have a bunch of kids be calm enough to sit around and game for four hours is to take 'em out and run 'em around first. We have a bunch of Nerf guns and Boffer swords just for this purpose. Kids have lots of extra energy and you need to figure out a way to bleed off some of that extra energy before you sit 'em down to game, otherwise you may run into crankiness. Of course, if you do too much running around, they may get distracted off into doing that, instead! So strike a balance.
One way to make the game interesting to parents is to have games on weekend nights so that they can have some "kid-free time" - gaming as a form of babysitting. Cool, huh?
7.) Your first game session:
* Talk about rules for interaction with the kids. Discuss how you are going to treat each other (hopefully with respect and courtesy). Discuss how you will keep everybody from talking at once (do you want to use a Caller, a person who is supposed to speak for the whole group (good if you have a child you can trust to not abuse the power) , or do you want to have them raise their hands and wait to be acknowledged (too much like school), have a talking stick (too new agey?), or just yell at them when they talk over each other (probably what you'll end up doing anyway). Remind them that this game is for them, that it isn't an "us versus them" thing, that the game is a team effort.
It's a good idea to get everyone's agreement at least initially as to what conduct is OK and what conduct is not OK.
* Ultimately, you are responsible for making the game as bicker-free and respectful as you can make it. If kids are getting bullied out of the way by older, more accomplished gamers, then you need to do something about it. If someone is calling someone else "Stupid" - you need to step in and solve it. Remember: you have the ultimate weapon. You don't need to yell, you don't have to get upset. All you have to do is say, "The game is over." That awesome power, albeit a nuclear weapon style consequence, is what you can use to keep order.
* It is easier to start really strict and hard-nosed and relax than it is to start relaxed and get really strict.
* Have players come with ideas for their characters in their heads. If possible, use a computer program to generate characters: it's much easier and quicker. Remember that most kids these days have grown up with very limited attention spans due to video games, television, and the Internet. So they will lose interest if you don't keep the pace moving.
* Make sure your first adventure session is exciting and interesting. Involve every player. Recognize that every player brings their own gaming style to the game. Some players will want to be purely social gamers: they will want to just sit there, roll dice when it's time, and listen to the story. Allow this to happen, but work to figure out what will intrigue them enough to get them further involved. Some people are just social gamers. That's not a problem - unless everyone in the group is unwilling to do anything in-game, which makes for a very boring time GMing.
* Make sure one player does not dominate the spotlight. Keep changing the focus of the story so that new people get to have their "15 minutes of fame" or longer.
* Don't let the kids rules lawyer you. Some kids are so good at memorizing rules that they will be able to quote, chapter and verse, from the gamebook. Don't let them control the game.
* Make sure you have food and drink on hand. Make sure you break for food and drink. Kids with sharply dropping blood sugar levels may get unreasonably cranky. Try to pick low-sugar snacks: popcorn is one of my favorites.
* Be fair. Be clear. Be swift in your administration of justice and your meteing out of praise and punishment. Let the kids know you appreciate them playing.
* Don't invite back troublemakers. They may change eventually, but they're not going to change if you don't draw a line with them. Make certain that everyone knows what will happen if the rules you've developed aren't followed. Make sure everyone knows what happens when you catch a cheater. Cheaters should never prosper!
I hope this helps! Let me know if you actually use this advice!