In my novels, the primary spirit, Margaret Plant, explains that spirits who have decided not to take the lighted path, but instead wish to live again, can choose to be absorbed into the body of a fetus. If this happens early in the pregnancy, the spirit may only influence the likes/dislikes/abilities of the newborn child. However, if the spirit is absorbed later in the pregnancy, the baby may actually retain memories of the spirit. Many call this reincarnation.
Watch these news articles and then decide for yourself whether or not Margaret is correct!