Kid packs come in a wide variety of sizes, and while you believe that yours are only a limited problem - "the key is to remember not to turn your upper body" - I've seen plenty that are. The one that we borrowed was definitely wider than I am at both hip and shoulder; wearing it in a crowded space would be much like wearing my trail backpack in a crowd.

There's also the fact that when the child is behind you, you can't see what it is doing. Busy little hands could be touching, grabbing, pushing and throwing and the parent might not have a clue.