My sister carries her 4-month old son at almost all the time of the day - whether he's awake or asleep. Usually the way she carries him is upward (chin rests on her shoulder). Is this a good practice? She's a full-time mom. But I'm thinking there should be enough breathing space for themselves too right?

Actually even animals carry their babies all the time. It's part of human nature and there's nothing wrong with it. Perhaps your sister may feel exhausted from the carrying, but may be she doesn't need the breathing space? Benefits of carrying baby: -Baby gets to see the world from your point of view and interacts with more adults hence learning speech and facial expressions more -Carrying baby around teaches them about balance and allows them to pick up motor skills faster -Less crying -Lower stress -Improved bonding http://www.marksdailyapple.com/why-you-should-wear-or-carry-your-baby/#axzz3z61QHcUN Probably she should babywear instead of just carrying baby so that she can have free hands to do whatever she needs to and also protect her back.