As a general rule, newborns and infants are best carried in a sling, wrap, or front carrier. Backpacks are better suited for slightly older and heavier children. Front carriers like the Baby Bjorn and the Snuggli hold babies against the wearer's chest, their head resting just beneath the chin.
Over-the-shoulder straps are attached to a carrier that supports a newborn's neck and shoulders. Some manufacturers have begun to add lower-back support. This is meant to accommodate heavier children and provide more months of use.
For the first four to six months of their lives, babies should be worn facing in toward the wearer's chest. After that, babies can be turned around to look out at the world. Most of these chest carriers accommodate newborns to toddlers weighing between 22 and 26 pounds.