> Kid gets off the school bus at the wrong stop: found in minutes.

if they have a phone they can call for help. before mobile phones they used payphones.

> Kid is riding bike, falls and knocked out:

Unless its somewhere very lonely, someone sees the kid, calls emergency services, who contact the parent. I do not know how this works in the US where you pay for ambulances though.

It's the same. Ambulance gets billed to insurance, if they don't have insurance then it's written off (actually just everyone else pays more).