I feel like if my job is to help produce productive, upright, and civil citizens then I should make them use manners to some extent. I firmly believe children should learn to respect themselves and others. However, manners are learned at home. I would be really concerned in early child development if a student lacked appropriate manners. I would make it first priority to meet with their parents, not to say that their child has no manners but indirectly receive some feedback as to how the parents behave.
Children learn from example.
Sometimes children may learn from peers and other influences. However, majority of the time it is learned through their parents. As a teacher you may find that both parents are busy working and not spending enough time with their child. A childs first years are crucial.