In my experience, the kids don't "get" homework everyday. When they age up to child or teen, their appropriate homework book appears in their inventory without the need to go to school first. The only thing going to school does is make them able to do it again. When children do their homework, they put it back in their inventory. The teens, however, do not put it back and leave it laying wherever they happen to be.
As Dellena mentioned, you can buy the book from the bookcase, but you might find that missing after they've done it as well. It's likely somewhere on your lot. I try to make sure they have an empty desk in a central location, and they usually go there to do it (but not always). This helps, but I sure wish they would fix this problem and make them put it in their inventory like the children do!
