Answer: The placenta (if the baby is unborn) and breast milk (if the baby is born and not weaned).
Explanation :
Alcohol that is ingested passes into the bloodstream of the mother and from there, it enters the baby through the placenta if the baby is in the uterus.
If the reference is to a baby that is born (and being breast-fed), alcohol is also found to be present in breast milk and hence enters the baby through that route.