There's a part of me that wishes I could find muzzles to fit my kids. Oh well.

I really don't use the leashes. I have in the past. There are some times it's just plain safer. I used one for DD#1 when at DS#1's ball games. She was at an age when she would scream bloody murder if in the stroller but would run off in the blink of an eye. No hand holding, no lap sitting.
I really should get one for the 2 y/o, but meh. I can just imagine her throwing herself to the ground, thrashing and screaming like she's being set on fire.

I wouldn't think twice if I saw a parent using a leash as long as the kid wasn't being physically dragged along.