Final answer:
Newborn babies acquire passive immunity from their mother through antibodies passed via the placenta and breast milk.
Step-by-step explanation:
Passive immunity is acquired naturally by a fetus through the mother's blood. Antibodies are transported from mother to fetus across the placenta, so babies have high levels of antibodies at birth. Their antibodies have the same range of antigen specificity as their mother's. Passive immunity may also be acquired by an infant through the mother's breast milk. This gives young infants protection from common pathogens in their environment while their own immune system matures.