The first story was when a friend was swimming with her kids at the gym. Her (I think at the time) four year old daughter was wearing only swim pants but no top. The staff asked them to leave since the girl (remember; 4 years old) did not cover her chest.
Similarly I was swimming with my (at the time) one year old daughter. She was only wearing these special infant pants that keep any accidents in (alternative to swim diapers). Another parent was next to me and started talking asking how old my son was. I can only assume the other parent assumed it was a boy since the one year old did not cover the chest.
Then recently we took the kids swimming at a beach. Afterwards at the car in the parking lot the kids (now six and four) started to undress to get out of their wet clothes. At this point I managed to get the kids inside the car before any of the locals got offended. I explained to the kids that they shouldn't get naked in the parking lot. Naturally they asked why... And sorry I blamed the US this time explaining that if we were in Sweden it would be OK but that people in the US didn't like it. The kids found it weird. Last I was in Sweden kids (before school age) were running around naked on the beach and nobody cared.
Now before you accuse me for encouraging pedophiles or something; I'm not encouraging anybody to force their kids to run around naked. And if they are running around naked at a beach there is a small risk they will end up in some perverted library where people get aroused by that. If you are not comfortable with taking that risk, don't let your kids run around naked. I surely wouldn't. The thing I do find ridiculous however (and something others relocating to the US should be aware of) is how a lot of people in the US expect even small girls to cover themselves as if they were adults. It actually scares me that people consider the chest of a toddler girl to be "sexual" enough that it should be covered up. But hey; maybe that is because I was brought up in a sauna with my best friend's family and all the girls in my class would swim topless until they were 15...