My parish has is one of the largest in the area and one of the largest catholic schools, I asked my nieces and nephews about this topic awhile back since they all attend school there just to get an idea on what they are being taught.
None of them really had a problem with it, they wondered more why older people seem to dislike the idea so much, I got the impression they all believed it was an outdated belief to be against SSM.
I think they are right, I do not think this will even be a topic of debate within 20-30 yrs, it will just be the way it is and nearly everyone will get in line with it, those that still try to argue about it will be viewed in the same way KKK members are today. (living in the past).
Well then, if I’m a Catholic Christian in my late 20’s, living in the year 2017… then I must
really be living in the past.

I also believe that sexual relations are to happen only in the context of marriage, and “no one” has really had a problem with sex outside of marriage for at least 50 years. I actually
waited to have sex for the first time on my wedding night. Man… I must be a
dinosaur, because I’m not living in the present, but in “the past”!
I agree with Ed: propaganda is being pushed in our schools, and in schools where the faith which was handed down by the Apostles is to be proclaimed, it is often silenced for fear of public backlash. Your nieces and nephews asked an honest question- “why are older people ‘dislikng’ the idea of state sanctioned SSM?” First off, I’m not one of those “older people” and
I can think of plenty of reasons why one should not support such attempts at marriage. Second, look into what
pluralistic ignorance is. Third, the quoted post is basically an “appeal to the calendar” a logical fallacy related to the “appeal to authority” fallacy. So what if it’s the year 2017? So what if a majority of people in our culture think that virtually any sexual activity “between consenting adults” (including those engaging in same sex activity) is morally permissible? If something is wrong… it’s wrong no matter how one tries to rationalize it.
What else do you think your young nieces and nephews are right on? Because many of their generation (that is, Millennials and Gen Z’ers) believe it’s OK to end the life of human beings that reside in the womb, and many believe it is morally permissible (or even
obligatory) for a young person with gender dysphoria to take hormones and other drugs to delay puberty, or to even castrate or mutilate their genitalia. Many teenagers also have no qualms about “hooking up” or finding random, one night flings on apps like Tinder. Do we think they’re right here too? Why or why not?
It’s like the old and tired saying, “If everyone jumped off a bridge, are you gonna jump off too?” Yea, no thanks. We shouldn’t be allowing a majority (well, a
seemingly wide, majority opinion as portrayed in the media) allow us to cast off immutable and unchangeable standards of the moral law, especially that which has been expressly revealed by the Church founded by Jesus Christ. We shouldn’t cast off our moral standards and “get in line with it”, especially if we know that “it” harms both the body and soul. But if one neglects to form their conscience or is not properly catechized, then it’s easy for the world’s ideas to take root, and again, with the rise of the “nones” it’s no wonder that these worldly ideas take root instead of what the Church has taught, and its reasons behind such teachings.