the only visiting girl I remember joining in the skinny dipping was their 7 year old cousin.
Visiting boys were more likely to swim nude. Some of the children visiting swam nude and some in swimsuits. Our neighbors often had their cousins and other friends visit.
She acted a bit surprised when they dropped their shorts, but after a minute they were playing together as kids normally do, both in the pool and on the lawn. The boys nudity was not much of an issue for her. Our daughter, wearing her swimsuit, swam with them and had a great time. Given that the kids were so young, we said we were OK with the boys skinny dipping. Their mother said wait a minute and asked us if she should send them into the house to get their suits or let them swim in the buff as they usually do. One of their sons asked if they could go in the pool. Our daughter wore a modest 2 piece swimsuit. Our neighbors who had boys aged 5,7, & 9 invited us over for a barbeque. We moved into a new neighborhood when she was 7. Our daughter swam in a swim suit with nude boys.