Raising an infant is an act of ecosystem engineering. You’re not just caring for a baby, but an entire world.
Right from birth, babies are colonized by legions of microbes that set up shop in their guts, skin, and more. These are vital. They help the growing human to digest its food, and to keep harmful microbes away. They are so important that newborns temporarily suppress their own immune system to give their microbial partners a chance to establish themselves.