I had no idea there was "discussion subreddits" on reddit. I always thought it was a site for hoarding karma by posting memes and puns.
But on a personal note, if you can't find interesting, intelligent content on Reddit, that is a criticism of yourself, not Reddit. Reddit houses some fascinatingly talented, smart, engaging people across a vast array of subject matter.
Should they be criticized by that?
Maybe take the time to share some of that interesting content here to parent to change his view instead of denouncing him. (https://xkcd.com/1053/)
The type of content that Reddit's design encourages most would be meme-blogging in the style of r/me_IRL