You use the term "bees".....actually I'm guessing you were experiencing "yellow jackets"...not honey bees.  There's no reason honey bees would be out in those open playing fields... However, yellow jackets live underground and often have their little homes in those open fields.  Additionally, this time of the year they are really unpleasant little fellows.  They're aggressive and their stings really hurt.  

Other than massive pesticide spraying....which I hope the schools do NOT do, all you can do is a)don't go barefoot and b) avoid the little rascals as much as possible.  Let's leave the honey bees alone, they're having a tough enough time surviving as is.  regards, Gary Crum