We be Goblins is pretty fun
I would suggest Crypt of the everflame. It has nothing that needs to be adjusted for children and the ovher all theme is one they will pick up one with the comming of age stuff.
We Be Goblins is actually a great introduction to Pathfinder, and can be a lead in to another full campaign, Jade Regent. So if it goes well you can move from it into the full campaign.
Alternatively you could purchase the Beginners Box and run that. While the rules are a little different you may find it better suited for younger players.
I wouldn't recommend We be Goblins as an introductory game.
Sure it's fun playing a non core race that is overtly evil. However, starting with a more traditional adventure will give them a better idea of the heart of the game. Masters of the Fallen Fortress is my vote. While not necessarily amazing, it's short enough to give a good introduction. From there you can get an idea of the play style of the players and decide what to do next.
Master of the Fallen Fortress - tower in the wilds
We Be Goblins - play a goblin; go crazy (great for 13yo boys!)
Hollow's Last Hope - wanna be a hero?
PFS First Steps: To Delve Dungeons Deep - on your way in, talk to the shabby one on the doorstep...
Pathfinder Beginner Box - everything you need to get them going and KEEP them going
But why stop at published material? Make up your own!
Scene 1: giant spider in the woods
- fight the monster
- discover a dead adventurer
- follow a Small sized trail
Scene 2: Crossing the stream
- use skills, teamwork
- learn to problem solve against hazards
Scene 3: faerie bog
- old growth forest with boggy interior
- warning signs by the fey
- another dead adventurer in a pond
- fight with a bunch of trained fire beetles; they use Aid Another and Charge to knock the PCs into the bogs.
Scene 4: hidden lair
- the trail ends near a gnarled old tree
- there's a secret door (DC 20 to notice)
- door is trapped and guarded by mites; fight scene
Scene 5: reveal - there's a whole dungeon here!
Then once they get this far and know the basics you can either stop or keep going. Depending on the boys' maturity and ability to follow plot, this can be as simple as a dungeon hack or as complex as you want it. You could have the mites be on their own. Alternatively you might reveal that some of the mites are in the town making people afraid. Why? Because they're being bullied into working for a bugbear who's hunting people by scent of fear.
You could use PFS rules; they're fairly simple, take care of the "how did we get here", "why are we travelling together", and "how do we divide up the loot" questions easily, and also make it so you don't have to track XP or figure out what is available to purchase, and don't have to worry about your kids playing an evil character. If you create PFS numbers for them on this site, you can submit the sessions so that when conventions come to town and they want to play in organized sessions, they can do so with their familiar characters. PFS scenarios are cheap, only $4 per scenario, and some are free. You can also run longer modules with the same rules.