It is civilised and a societal norm in British society to wear clothes. If you bung a child into a pool and flume with a load of naked adults that they are not related to this, IMHO has the potential to ‘cause harm’ to that child.
I agree it is a societal norm in Britain to wear clothes, but something being a 'societal norm' doesn't make it right. 100 years ago it was a societal norm for women not to be allowed to vote - does that mean it was right?
In some cultures, a far greater level of modesty in dress is the societal norm. While it's to be hoped people from other cultures would respect those beliefs, that doesn't mean that everyone has to agree it's wrong to show, for example, your bare legs.
What I'm saying is that it's fairly arbitrary which parts of the human body it's deemed acceptable to show and there's no inherent moral reason for anyone to conform to the norm of their particular society - unless non-conformity harms others.
Walking naked through a public park - yes, might shock or harm others, not acceptable in British society. Attending/organising an event which is clearly advertised as being for nudists - no one is going to be shocked - therefore, it's acceptable