It certainly is a grey area, most beaches have topless sunbathers a few have well defined nude areas but walk down the street or into a shop topless someone is going say something for sure.
Films and TV are censored so that children don't see nudity I think it is quite reasonable for them not too see it at the breakfast table. By that logic I would ask them not to appear naked because it upset the children, if they then repeated the nudity it would have been intentional.
The same applies to noisy neighbours, ask them to stop, if they repeat it they are deliberately being unsociable, the vast majority of us are considerate neighbours but there are a few that don't care.