Newborn onesies really are a staple apparel item for infants and toddlers, widely well known throughout the United States. They can be made to be snug, practical, and easy to use for both of those moms and dads and babies.Precisely what is a Newborn Onesie?A toddler onesie is a 1-piece garment that covers an infant's torso and snaps in the crotch.