They are generally one size fits all, and are a great option for use with newborns and little babies. They mould to babies backs keeping the natural curve in their spine. They are safest to use in the upright position, tummy to tummy with you. They generally require more than one layer of material over bub when they are wrapped, and can be used up to around 14kg (depending on brand). You may however find that when bub does start to get bigger the wrap will not be as supportive, and may need to be tightened a little more often. At this stage you may like to look into getting a woven wrap or an Structured carrier.
Please contact us if you would like any help in choosing!