Grumpy Kids???

Every afternoon at 3:15 the county scholl bus passes the farm. I am usually getting the cows in to milk and 90% of the time I am close enough to give a friendly wave. I have never seen my act of friendliness reciprocated. Is this a common problem? Why do these children seem so listless and uninterested? Why do they stare out the window and see nothing? Am I the only one who has had this expierence? Quite frankly I find it annoying. Like a slap in the face. An attitude of disrespect and unfriendliness. Of course I may be wrong.