A special sleep secret
Melatonin is a hormone that your brain produces in response to darkness. It helps with the timing of your circadian rhythms (24-hour internal clock) and, Not just in adults, but even new born babies have their sleep regulated by melatonin. But it's their mother's melatonin that affects their sleep initially.
Breast milk contains melatonin, and its levels change according to time of the day. Breast milk at night contains a higher level, likely to train the baby's circadian rhythm.