At the bottom of that link, in italics, the author is acknowledging the point I am making, i.e, that the family saying they didn't know about it isn't the same as saying it didn't happen. I think it is very plausible that he simply didn't tell them, possibly out of embarasment, or a desire not to bring home troubles he had with being different, particularly to an older sibling away at college.
That said, I think there is considerable doubt that this incident happened or at least happened the way the hatchet man described it. And even if it did, it doesn't say anything of importance about Romney's character or ability. He has lived an adult life of considerable distinction and character in my opinion. certainly enough to qualify him for the Presidency.