Showing up nude in public where there also happens to be warm water, a pleasant wind, and naked females romping about will make your son’s arousal significantly more likely.
I would recommend that you simply refrain from insisting to your wife that erections do not occur at nudist places, particularly among teenagers, because that statement is way off http://hqnudism.com .
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 boy is extremely likely able to sense your requirement for secrecy in this matter and that fact alone will make him uneasy about it, or even embarrassed.
The next time he gets an erection in your existence, be casual about it. Tell him it’s part of life, there’s nothing wrong with having one, he’s a completely normal lad and there isn’t any demand to be embarassed. But do highlight the requirement to act appropriately if (when) it happens around others, by not waving it about like a huge flag and to just dismiss it if he can not easily hide it. Not bringing others’ attention to it is http://nudistsass.com of action. If a person does notice, he should stay cool as if nothing is going on.
And as one poster already suggested, be sure your daughter doesn’t make fun of him if (when) she sees him with an erection. Thirteen year old boys can be quite sensitive about those opinions.
In addition , I suggest having a talk with “the wife” and acknowledge the information you gave her isn’t completely right. She will nearly surely see your son with an erection one day at the resort. She needs to know he’s having them, and supplying 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 teenage boy, she is able to take it in stride when it does occur and not make your son feel lousy about an uncontrollable body function.