Of the 840k games on itch only 0.2% are nsfw. Itch is not flooded with nsfw games, it is flooded with games.
And same with google, you need to change options to see the nsfw stuff on itch. As you obviously did. The relevant options is named "(x) Show content marked as adult in search & browse" on the front page of your settings/profile.
You actually should be flooded with horror games on browse. Those are not appropriate for children either, so I shall claim, that children are in fact not the target audience of itch.
That being said, there are regular attempts of bad agents to upload malware and stolen games. Those are typically nsfw. If you see nsfw despite having it turned off and not seeking it out specifically, it might be one of those.