(#429)this is not just scratch it happens on ROBLOX, YouTube, twitch and any site with user generated content so on some sites you need parental controlsSupport! But the thing is I don't think there are any non children friendly project or studios.There actually is a fair amount, but moderation tries to remove them. Sometimes they are up for a while before they end up getting taken down though, so there most definitely is on Scratch.
ROBLOX has terrible moderation. It also has 17+, 13+, and 9+ games on there, and people younger than those ages could play those if they just select the wrong birthday on sign-up.
YouTube is already designed for 13+ but does have kid-friendly content, and allows minimal swearing and inappropriate jokes. It's a bit of a mix so parents might want to use Restricted Mode or YouTube Kids.
Twitch is for 13+ only.
Not all sites need it. Scratch isn't a social media. All of the above you mentioned are video games or social medias.