Ideally, no matter what the size of the platform is, if it's genuinely impossible for the people running that platform to not harm children, that should be thei

Ideally, no matter what the size of the platform is, if it's genuinely impossible for the people running that platform to not harm children, that should be their problem. If they can't figure out how to not be harmful to children, they don't get to exist. That's how it's supposed to work. In practice though, it's not unreasonable to say that we should expect more from companies that can cause harms at a much larger scale. Perhaps there's some kind of threshold where we can accept some harm being done at a small scale while still not allowing harm at a much larger scale. Seems fair enough.