You talking about kids under 6? My daughter was a petite 7yo her first trip to Alta. No issues for her. She was an intermediate who learned to ski in the southeast. Was able to ski the blues on the Albion side after a day or two of ski school.
I'm talking about 4footish younguns that can't reach the footrests and can't sit far back on the chair sliding forward - either they know to push the bar *hard* while at the same time leaning /forward/ (quite counterintuitive for the kids I was on the chair with, apparently) or the parent is doing a straightarm back-of-collar lift.
I don't know if it's the chair dimensions or the surface resilience but Alta is the only place I've seen (and had to help with, multiple instances of) this scenario.
What footrests? Snowbird lifts have footrests but not at Alta.
The change that Alta made for kids on the lifts several years ago was to add short bars that can go between legs so a little kid can't slip out underneath. Still no footrests.