1st session
Had the first session today. I'm not the most prosaic writer, so don't expect any story hours here

. I did want to let you folks know what's going on and what we did. Any feedback is appreciated.
My 7 year old son decided to play a human fighter.
My 10 year old daughter chose a human druid.
My 3 year old daughter chose a halfling rouge (with some help from my wife, and being told that a halfling grownup is shorter than she is

.) [The character is primarily played by my wife, but gives my daughter the sense of participating in our game. She can't wait to roll the d20 when told to.]
And my wife chose a human sorcerer. This is the first time she is playing a spellcaster. She normally plays a fighter or rogue (or ftr/rog).
I went with the Hogwart/Door idea, placing the group in Throckburn's School for Young Adventurers. It surprised the players a bit that they weren't going to be "hardened adventurers" but they seemed to get into the spirit of things. They were all at a new school and didn't know anyone. The characters made friends quickly; you could see the party cohesion forming already.
They learned the three rules of Throckburn's:
There are three rules you must remember while at Throckburn’s. Any violation of these rules will result in immediate expulsion:
1) No fighting outside of training sessions.
2) DO NOT enter any door that is not Blue unless instructed to do so by a professor.
3) Training sessions must be reported on in full by the next day, including a complete recap on encounters and on items retrieved.
After some NPC interaction where the kids did a great job at roleplaying, they were brought to the first door by their instructor: Green Door #12. (There are 5 door colors at Throckburn's.
Blue - Standard, normal door.
Green - New student door (1st-2nd level).
Yellow - Middle Student door (3rd level).
Red - Upper classmen (4-5th level).
And finally, Black - Graduation exercises and places where the instructors brush up their skills.
Students are magically monitored and in the case of TPK's, retreived by special retreival squads.
At the door the PCs were each given a potion of cure light wounds (I created item cards using ink jet business cards purchased from Staples. The kids loved it. See this link:
http://enworld.cyberstreet.com/showthread.php?s=&threadid=35181 ) and told that there had been some disturbances reported from the area they were going to. I then ran the group through "Hollow Threats" from Dungeon #96. The kids and my wife had a great time. It was really fun seeing my son roleplaying the interaction with the NPCs in the adventure. It was also great seeing their faces lighting up when they defeated the antagonists and went through their rewards!
They made me promise that we would play again on New Year's Day.
Anyway, the Adventurer's School concept works real well for a kid focused campaign. It gives them a "safe" place to start from and return to, and allows them to get assistance when necessary without stressing the suspension of disbelief. They also don't have to look too much into the campaign world to see what's driving the game because they are being sent all over the place by their school, while still having a consistent feel to it. By they time they "graduate", which should be about 5th level, they should have enough exerience in gaming to begin to appreciate more complex campaign structures.
If people are interested, I'll continue to post on how the campaign and the kid's gaming are progressing.
--Sam