Baby Carrier One can be used from birth (at least 8 lbs/3.5 kg and 21 in/53 cm) up to about 3 years (max. 33 lbs/15 kg and 39 in/100 cm). The leg straps should always be used when your child weighs between 8 lbs/3.5 kg and 10 lbs/4.5 kg. Your child should always be carried facing inwards until he or she can support his or her head on their own, usually around five months of age. Your child can start being worn on your back after they are about 12 months old.