Final answer:
A child tracing lineage through only the mother's side is part of a matrilineal society, where inheritance and kinship are determined via the female lineage.
Step-by-step explanation:
A child who associates his line of descent with his mother’s side only is part of a matrilineal society. In such societies, family ties and inheritance are traced through women, with the maternal lineage determining clan affiliation and the passing of property and status. This system is found among various indigenous peoples in North America, like the Crow and Cherokee tribes, and ensures certainty of maternity for tracing kinship, as opposed to paternity which can be more uncertain.