And idea for you, if the kids in your group are playing characters who are also kids . . . .
The child of a local butcher, inn-keeper, or other merchant who has access to food, has been acting strangely, from the point of view of the characters (but not from the point of view of the town's adults). The kids can't get any adults to listen to them, so they have to investigate on their own. Simultaneously, the adults in town are busy dealing with some disease or something that's causing many of the people to be sick. The kids watch this other child who, it turns out, has been going off on his own and heading into a cave somewhere just outside of town. In that cave, there's some bad guy (pick whatever enemy seems suitable to you), and this bad guy has this kid under a charm. The bad guy has it in for the town for some reason (adventure hook for the next session), and is using this kid to help him poison the city's food.
The kids find this out, but can't get anyone to listen to them. So, they have to solve the mystery on their own. They gather up some stones or clubs (or whatever you deem appropriate weapons for 11 year-olds) and head into the caves. Luckily for them, they don't confront the bad guy--he's out at the time. Maybe they have a frighting run in with some rats or spiders (no poison saves though--not on the first adventure). But, they find some books or notes, written in some strange language.
One of the kids is the son of a librarian or of a mage or something. They sneak into the parent's stuff and decipher the notes. The notes are the formula for the disease, from which, they hope, the formula for an antidote can be found.
Another kid is the child of the apothecarist, or whatever, and they sneak in there to get the stuff. Once the kids make the concoction, they sneak it into the food supply and people start feeling better.
All the while, the other kid hasn't been heard from in a while. The now braver adventurers decide to solve this puzzle by going back to the cave. Afraid of what they might find (the notes make them think they're dealing with a powerful wizard), they go to one of their homes and get their family's guard dog to come along. While there in the cave, they find that the kid is in a cell of some kind--apparently he'd outlived his usefulness, or he's being kept here so he won't be hard to find later. The bad guy isn't around, but as the kids are trying to free the child, or break the charm, or whatever, they hear the bad guy returning. They're cornered and have to fight. The kids do a valiant job, and the dog really helps.
Maybe when the bad guy trips (from the dog?) he gets knocked out and this ends the charm. Then the kid in the cage tells them where the key is. Clever kids that they are, they manage to subdue the bad guy and trap him in the cell that the other kid was in. Now they all go back to town. They'd been missing for a bit too long and so a search party finds them. Finally, the adults listen and go into the cave, finding the trapped bad guy.
Everyone praises the kids for their bravery (except for the moms who keep fanning themselves and telling the kids they shouldn't do this anymore), and the bad guy is dealt with by the adults.
Dave