have you seen the hive? if not, i'll hazard a guess that they are not bees. they are probably yellow jackets and stirred up out of the ground by the kids riding.
they are very aggressive at this time of the year. if you can not get someone to identify them for you ASAP, go to the feed store or hardware store and get a couple of yellow jacket traps. put them around the edges of your property, especially on the field side.
if you want to try to identify them for yourself, take a piece of meat (big enough that they can't carry it off, but not toooo big) and standby back to watch. yellow jackets will swarm meat in short order. honey bees will not.