It's not Reddit's fault, it's not the mod's fault, it's not anyone's fault but the parents. If you cannot make sure that your child will not find thicc thigh bitches getting railed in every way imaginable, then you can only expect that your child will find it on their own. If you fear that safe parts of Reddit will link to unsafe parts, whether it's from moderators, staff or users, then you're better off keeping your child off Reddit. After all, Reddit is a M rated app, for people 18 years of age.
Oh and why would you let your child near Doki Doki Literature Club if you do not allow porn as a parent?! Doki Doki Literature Club is not a game for children, and frankly, porn is the least of my concerns when 2 out of the 4 characters graphically take their own fucking lives in the fucking game!!!! I don't care that it's not real, if you child cannot believe that porn is all an act, then why would they think that the game is any different!?!
If the mods at the other subreddit wanna link to this one, then I say let them do it!
TL;DR version
Reddit is an adult app, even if not all parts of the app contains adult content. As a parent, it is your duty to make sure that your child cannot access adult content. It is not our fault, and it is not our job to babysit your kids. Also, if you oppose the idea of pornography, then you should also oppose your child going anywhere near a game with suicide.
The pack I linked is free and includes the DLC and several mods.
Regarding the original game, it's near impossible to purchase. I can't find any (official) downloadable version online. I found this hard copy on Amazon, but I don't think over $100 going to people with no reviews is reasonable, not to mention I don't think it includes any of the DLC, has no translation and your final product might not even work.