In our culture, children are taught good manners even before reaching school age. Parents teach by showing their children how and the why was explained. For example, the kissing of the hand of the elders, it is a sign of respect that should be practiced by children even when they are grown up already. And in the urban areas, children should know how to act with grace when in public places courtesy of their parents. That’s why unruly teenagers give the impression that their parents have neglected them.
I think teaching good manners is a good idea, and with these children-it should then become a good habit that they can use for the rest of their life. I think starting early as possible is a good idea-so they can become automatic as the child grows up and goes through life. Also its important for them socially because there are many advantages to behaving well in society-and I think consistency is important as well when you teach your kids. It may take awhile as you practice and reinforce them-but it will do them a lot of good !
My parents tried to teach us values and manners early on, although they don't really practice what they preach, because they swear whenever they were angry, and would not hide their fights from us. But despite that, my brother has remained courteous and polite to people, so I think manners are also inherent.