D&D with kids

My oldest son, Spencer (13) has been showing a fair amount of interest in Dungeons & Dragons for a little while now, so on a whim I whipped up three third level characters, and asked my kids if anyone was interested in me running them through a little sumthin-sumthin. Spencer and Alexander (7) both responded positively; Jessica (11) wasn't interested at this point, which was fine, although I think she might have enjoyed it. I had characters for the three of them whipped up, a human sorcerer for Spencer (I figured he was old enough to handle the added complexity of casting spells) and a human ranger named Ormando for Alex. I had a human rogue (Carlota) for Jessica, and maybe Carlota will get some action before all's said and done yet.

We only had about an hour to play, but stealing some names and ideas liberally from the Golarion setting, I had them set out from the Academy in Absalom, recently graduated, and offered a job as security/sherrifs at the small, frontier town of Sandpoint. While travelling, their riverboat was attacked by bandits; two on the shore shooting arrows and two on a boat coming over to board them. They handled them very well; Spencer's character Bendek took a few arrow wounds, but his spells also managed three of the bad guys quite well, while Alex's character shot his bow very poorly, but managed with longsword and tomahawk to way overkill the last bandit, who was threatening them all on the boat.

A young passenger flirted with them after this a bit, the mayor of Sandpoint congratulated them on a good start, put them up in a nice little cottage on the edge of town, and then we were out of time.

The kids enjoyed the combat most of all, but did also enjoy the roleplaying activities a bit too. I think it went well. Both were intersted in playing again on Sunday (which we did not have time to do, and now Spencer's at Scout camp, so next weekend at the earliest before we can follow up.) We'll see how it goes.

Anyways; any ideas on where to go from here? I'm thinking of maybe starting them off with some kind of little mean-spirited fey or goblin like creature who's kidnapping children and hiding them in the crawlspaces of the town, or in a cave in the limestone cliffs just out of town that they have to deal with, but other than that, I'm flying kinda blind.