The fruits of labour of a migrant farm worker who has planted his seed in the garden of an unsuspecting local (usually a fat white chick with low self-esteem). After nine months of careful nurturing, a young seedling is born around the time of Thanksgiving harvest. This token of success is an easy way for migrant workers to gain immigrant status.
Henry: You know that Donavon kid from school? Have you ever wondered why he has a fro?
Johnny: Didn’t you know?... he’s a harvest child.
Henry: Oh ok, I guess that also explains why he tans easily.