In Just Babies: The Origins of Good and Evil, the author argues that the seeds of morality are very much built in, and visible in even tiny babies. And it turns out that babies will easily choose the helpful puppet over the one who is acting meanly, that toddlers will try to console upset children and adults, and that young children delight in tattling so wrongdoers will be punished. The author does not shy away from the less happy side of inborn morality, especially the consequences of preferring the in-group to others.
For me, the best part of the book was the story of experiments with small babies, requiring much ingenuity. But I felt that they were much better described in Alison Gopnik’s books, especially The Scientist In The Crib: Minds, Brains, And How Children Learn, so I would recommend them instead of or in addition to this one.