K.M.
Are you sure it's not his canines or the lateral incisors coming in instead of the middle teeth? Not all children have the bottom teeth come in and then the top 2 afterward. Our daughter had the bottom middle 2, then the top 2 laterals, then the upper middle, then the lower laterals and now she's getting all of her pre-molars before the canines. Have your pediatrician check them the next time you are in but it sounds like they are just coming in out of order.