Warm milk may help your baby sleep better. If you are nursing your baby, your milk is already at the perfect temperature. Pumped milk or formula may be warmed, and temperature tested by dropping a few drops on the inside of your wrist. Never use a microwave to warm milk. In the evenings, breast milk has higher levels of melatonin, the sleep hormone. If you pump your milk, it may help to label your milk with the time you pumped it, so you can feed your baby melatonin-rich milk in the evenings and at night.