Patterns for babies need two things from your yarn: it must be soft enough to sit against newborn skin, and it must be machine-washable because babies make messes. Most yarn manufacturers label baby-suitable yarns clearly โ look for cotton, bamboo, or superwash merino blends.
Preemie hats use very little yarn (about 30โ50 yards) and make a generous donation gift for NICUs. Standard newborn hats are 12โ14" head circumference; a 0โ6m baby is 14โ17".