Bonnie, slings can be used to keep a baby upright as well as other carriers
can.  I find that most babies prefer the upright, chest-hold use of the
sling and I demonstrate that for the mothers.  In cultures where slings have
been used for a long time, babies are held upright taking care of air
bubbles and any stomach distress.  ("What do Americans mean by 'burping the
baby?'") We Americans just see a sleeping baby as a horizontal experience.
The doctor who advocates "wearing" babies shows many positions in his
brochure; whereas the material that comes with slings bought in most baby
stores shows newborns lying down and larger babies upright.

We are learning.

Pat Gima, IBCLC