"If your kids coach said he wanted your kid to come over after the school was closed and everyone was gone for a work out and shower would you let him or her?"
When I was in school, this happened all the time. Now this was the 70's but the time when this all changed was 2002 after the Boston Globe blew up with the institutional issues of the Catholic Church.
In my school, coaches had unfettered access to the gym. Often, coaches would stay late to work with players in all sorts of athletics. Then, they were supposed to shower. Some schools had separate facilities for players and coaches, others did not. It was pretty common. I, as a teen, participated but don't recall ever being approached by a man at all. I do recall being groped by a dude who used to cut my hair (he'd drop his comb on your lap) and a local tailer (who'd check to see if you had enough room in your crotch). We used to laugh about it.
+1. In 7th-8th grade (75-76) our gym teacher showered with us.