The idea wouldn't work in practice.
You'd need a day off work to do so, you'd need to travel quite a way unless the university is nearby, you'd need to care about your son's education and career (not all parents do).
Some would say it's positive discrimination, it's all universities having an open day where female prospective applicants aren't invited.
And if this all happens on the same day nationally then footfall at each university is going to be pretty pathetic.