When I start the game there's almost always several kids stuck in the ocean, and often some in the pond underneath the waterfall, as well. I expect as your population grows you'll start seeing more caught there, too.

I don't so often see them stuck on the roofs. I do remember one time though when I'd just started a new game and the first hut got to 50% and sprouted the framework. It caught both builders and the farmer who was passing with a fish. That was all three of my adult villagers stuck!