I bet you anything that new rule gets walked back before the end of this school year. Let the lawyers and school administrators figure out an acceptable level of liability. I presume many children would feel better with at least one adult present. Although the students may not want to admit it. Even a group of the nicest school kids can get too loud or too goofy when on a field trip. Or one student may not have any friends to hang with, so they need teacher support.
Over here, they need a teacher with a sidearm handy. Goofy kids are the least of our worries.