The infant milk from the mother is more than just a source of nutrition for infants; it also acts as a clock that teaches them what time of day it is. The baby's need for breastmilk dictates the mother's supply. As the baby eats more, the breast will produce more milk.

Every day, breast milk goes through significant changes. Cortisol levels in morning milk are three times higher than those in evening milk. The highest concentrations of magnesium, zinc, potassium, and sodium are in the morning. Day milk has more amino acids that encourage activity than night milk. While the iron in milk reaches its peak around noon and vitamin E in breastmilk is at its highest in the evening. 

The hormone melatonin, that aids in digestion and sleep, is hardly noticeable in milk consumed during the day but increases in the evening and reaches its peak around midnight. Additionally, some DNA building blocks found in night milk are present in higher concentrations, aiding in the promotion of sound sleep.

The sleeping and waking schedule of a child can be difficult for some new parents. Many people hold the opinion that feeding infants solid foods may promote sound sleep. However, studies show that in order to promote sound sleep without feeling hungry, a child needs to be well-fed during the day. This will help reduce the frequency of a child being hungry at night. (DMOIIParreño/NOIIIFlores/RNPCLaquihon)

References:

https://dornsife.usc.edu/news/stories/3060/breast-milk-helps-babies-tell-circadian-rhythm-from-mom/