Purchase some corkboard squares at an office supply store, and mount them to the walls around the desk. That way, your kids can post materials and homework-related papers on them for convenient reference. But, make sure you keep the postings limited to minimize distractions.
Also mount at least one shelf on the wall where textbooks can be stored within easy reach of the study area. A standard desktop calendar blotter is an important accessory, too, because your kids can jot down homework due dates and other school matters and keep them in sight. Finally, add a small table lamp that provides plenty of good light for reading.