MOST crossing guards sit in their cars, as we are out there a long time (up to 2.5 hours) and there are stretches of time between groups of students.
We were told not to by the administration, but the police officer who oversees us said it was okay. I mean, most of my coworkers are old and it gets cold out. My friend is in her 70's. She does have a tendency to miss people. Most of the kids are accompanied by their parents, though.
I prefer to stand outside because I would otherwise get distracted and not see the students.