I have no issues with no socks. I too go sockless all summer long. Kids feet are probably cleaner than their hands that they stick into their mouths, up their noses anyways.
If parents bring them with socks, and if they don't mind, I often take them off, because my little ones like to do that and hide them anyways. They can wear soft slippers if they want, but no running shoes allowed. Too easy for little fingers to get stepped on. I wouldn't mind if they are older, but with young ones that are on the floor mostly, it's just not a good idea.