If your property isn't being damaged, then what harm are they doing? this country nowadays is hellbent on getting people into trouble or reporting them for something or other, When me and my brother and sister were growing up we always played in the road, football, cricket (soft ball) rounders etc balls were always going into gardens but we used to appologise and carry on, there were never any repercussions, yes I know things are different now but don't you think that all the fuss people make over little things such as a ball in a garden just contributes to this change? Try turning a blind eye.