I blame the current fad of using a sling for a lot of the physical issues. If your arms and legs are imbolized you don't use them. If your body is constantly supported by the sling you don't develop strength in the upper body. Now dont' get me wrong I think a sling has it's place for newborns but once a child should be mobile it's use should be discontinued at least for portions of the day. I have had a mom come for an interview and carried her 11 month old in in the carseat and then transfer her to the sling for the duration of the interview. Other than the cute little face and the brief view as she was lifted out of the seat I never saw the child the rest of the time. Any attempts to get access to the child were met with a why kind of response. Needless to say suggested a nanny at least for a few months till child was a little more independent as there was no way this child was ready for group daycare.