Kenny's position certainly seems driven by some amount of reactionary social conservatism. This is a no-win, dead issue for them. Move on to substantive policy issues.  Old Martha and Henry on the farm might vote for him based on this but to plenty of other people it just looks like legacy homophobia. To my understanding, no other school club requires parental notification as a matter of policy. Last I checked, it's a free country and  kids join the clubs or associate with whomever they want to.
The future Premier's implication is that the kids joining these clubs are in crisis or having some sort of mental issue. If that is the case it should be supported by some data or even a groundswell of anecdotal evidence, I'm not seeing it. Even with that, this issue is still an electoral loser for them and just creates needless friction with the moderate and progressive elements in the PC party.