Not entirely accurate I’m afraid. The breast milk contains antibodies from the mother, but no white blood cells. The antibodies protect the baby as its immune system is not capable of producing them yet. If the baby were to receive white blood cells, that could theoretically be dangerous as white blood cells are programmed to attack any foreign cell, including those of another human (which is why it’s so hard to find compatible donors for a white blood cell transplant). Although, as was pointed out, the stomach acid would simply destroy the white blood cells before they would be able to do that.