Teaching ethics to a small child is absolutely appropriate. There is no better time to begin teaching the concepts of moral right and wrong. Of course always teach to the level of the child and be sure to listen to the responses to ensure the material is being received. I would teach the concrete message and not the philosophy.
Civics, not so much. Social studies seems to be well placed in primary school. If the child expresses particular interest, however, I always believe in providing as much answer as needed to satisify the questioner.