Showing up nude in public where there also happens to be warm water, a nice wind, and naked females romping about is going to make your son’s arousal significantly more likely. I suggest that you simply refrain from insisting to your wife that erections do not occur at nudist sites, particularly among adolescents, because http://kazyz.com is way off the mark.
You commented that you did not mention anything to your wife about your son’s erection in the water (“I never told my wife.”) The lad is extremely likely able to feel your need for secrecy in this matter and that fact alone will make him uneasy about it, or even ashamed.
The next time he gets an erection in your presence, be casual about it. Tell him it is part of life, there’s nothing wrong with having one, he is a completely regular lad and there’s no demand to be embarassed. However do underscore the requirement to act appropriately if (when) it happens around others, by not waving it around like a large flag and to just ignore it if he can’t readily conceal it.
Not bringing others’ focus to it is the best plan of action. If someone does notice, he should stay cool as if nothing is going on.
And as one poster already indicated, ensure that your daughter does not make fun of him if (when) she sees him with an erection. Thirteen year old boys may be quite sensitive about those remarks.
In addition , I advise having a chat with “the wife” and declare the information you gave her isn’t completely right. http://x-nudism.com/demo1.php is going to almost absolutely see your son with an erection one day in the resort. She has to know he is having them, and providing right info on the topic will reduce her shock and embarassment. In case your wife understands how likely and normal erections are for a young teen boy, she is able to take it in stride when it does happen and not make your son feel lousy about an uncontrollable body function.