I have done this in an elementary type setting, principally grade 5. I've also been hired to run for kids' birthday parties.
I suggest keeping things simple, and you should probably keep out some rules. Like don't penalize kids for striking to subdue. Don't mess with some of the tedious rules, and perhaps have items that allow that to work (like give someone a bag of holding or such). For treasure, have items that are a bit grander than you might normally have--like an axe that can cut through anything, or boots that let a person walk on air as if walking on the floor, or move twice as fast as anyone else. Dole out lots of situational bonuses for creative teamwork or ideas, or even attempts at creative teamwork or ideas. I'd expand those bonuses, too--give a range of +2 to +10 or even more. You want an immediate reward for the kids--positive reinforcement. (A +2 bonus is pretty crummy because the kid will only appreciate it about 10% of the time, thus I'd make it significantly higher.) Tell them expressly that you're changing some of the rules based on discussions with other people--after all, house rules are a major part of the game, right?
Be sure to plan ways for everyone to get some spotlight at the table. And be prepared to come up with some improvisational ways to give people spotlight, as some kids will naturally budge some of the others out, and not because they are malicious or anything. If a kid is smart enough to understand the value of sharing spotlight time and enabling other people to have a good time at the table, give that kid a huge something.
Aid another is always nice. Insist that they narrate how, though, before they can do so.
Where there are more than 3 choices, decide ahead of time. Like summon monster--make it only two monsters available at each level, at least for starters. Or with spells available--limit the choices down. Do this to focus their strategic choices, i.e. something that flies, or something that is tough and has a sense of smell.
Expect that many of your kids won't know certain vocabulary words so well, like "diplomacy" or "bluff."
Simple puzzles and riddles are good. It's okay if they're too easy, as the success can give momentum. You can set them up with several avenues to success.
More than combat, I'd be very careful about religion. I wouldn't do it. At all. Give the wizards and sorcerers healing spells. (Merlin had them, after all.) A druid is maybe okay, but personally I wouldn't even go that far. Don't give paladins a god--just have them be some virtuous knight of the realm.
Along that same line, I'd lay out some simple ground rules about the intent of the game. The game is about heroes, and you will reward them for being heroes and for teamwork (and then follow up on that with those bonuses).
Honesty is important to them, so I would roll in front of the screen where practicable--especially for enemy saving throws and things that don't hurt the PCs, or where there is no chance of death (2d6 damage and the character has 20 HPs). Fudging dice rolls in the interest of momentum at the table is required, though, of course. I would keep bleeding and death in the game, myself, as those are part of heroics and the basis of teamwork at the table.
Keep the enemies as monsters. Don't kill people, even bandits. Defend a town-type things are good, or save the princess from the wizard with goblin slaves. Grand, simple stories. Make sure everyone has stuff to do, although it doesn't always have to be awesome--so make sure there are some wands and such.
Selling points? Math. Probabilities. Using scarce resources. Puzzle solving. Teamwork. Vocabulary words. Talk up the probabilities at the table, and their choices. So much of this game orients on combat--that's where all the strategic and tactical decisions lie. There's very little strategy in skill rolls--you can only hand out bonuses for narration, and there's no strategic choice there. I would probably use another system myself, frankly, but I imagine Pathfinder is one you know and one you want to roll with, and that's cool.
These are my thoughts. I hope they're helpful in some way. there's more but this is all I can think of for now.