REI.com is currently running a sale on their selection of baby backpacks. I'm not looking for a product recommendation because ultimately that's like asking someone's favorite flavor of ice cream. What I am interested in are people's recommendations on what to consider when purchasing a baby backpack. We live at the foot of one and near several mountain ranges so do a fair amount of hiking. We have twins so can make concessions on one backpack (better for mom, roomier etc.) if we can make them up in the other.
Are there better positions for the baby to be carried in? How much room for carrying stuff is necessary? Is there anything in particular to stay away from? Are particular bag features safer than others?
My twins are 3 months old, but were two months premature and currently both are just over 9 pounds. Even if we cannot use the carrier straight away I'd like to purchase two during the sale.