Hmmm, sounds like the boy has learned to stay innocent.
Wouldn't it be nice if everyone could stay innocent & not be eiether ashamed of their bodies or too easily sexually excited by mere nudity.
His parents obviously believe that nude is not the same as lewd, and since people are made in God's image, can we really say otherwise? What matters is the heart.
Nevertheless,...if it offends you, don't look at it,...or, consider just why you feel offended by it. We are the product of our society, our parents beliefs, and those of people around us, as well as common habits & customs. Don't yuo yourself get aggravated when people do something you consider ridiculous simply because..."we have ALWAYS done it that way"? Take awhile to ponder & consider the pros & cons of such a matter, honestly -- you know, try to convince yourself as if from both sides of the argument. There might be a surprising revelation or two in there somewhere, both for you and for him/them.
If you knew it were somehow beneficial for him would you be able to not be offended for his sake?
if his family are nudist's why are you looking to see if a young boy has an erection?
It would appear that the child is being raised as a nudist.
If a display of this manner is illegal in your country,
report it to your local law enforcement.
If it's legal... tell the parents that you can see "everything"
as they may not be aware that they can be seen.
Or, you can simply look away.
Because the police hasn't gotten a hold of the parents and charged them with neglect and abuse!!!
I question you "He is seen with no erection at all"...why would you make that comment?