I think that the difference may be that there's relatively little benefit or desire to researching children falling out of planes and we have fairly easy ways to study the question indirectly (accelerometers, cadaver studies, animal studies, etc.).
Also, there are numerous examples throughout history of people performing evil human studies; so while people may not have studied children falling from planes, people have studied equivalent things.
Without directly addressing your proposed experiment, the history of aviation was filled with all sorts of grotesque experiments on humans. Absolutely disgusting stuff, like suffocating people to simulate high altitude flight. There was an ethical quandary about whether to use this data (IE, as citations).
If you can't get funding for your research, or publish under your real name if you do, it's certainly going curtail research at least. It could still happen if some nations refuse to endorse the ban, but there will at least be less of it, which means less risk.
We're not talking about a targeted weapon, we're talking about accidentally unleashing an unstoppable global pandemic. If only China is risking that, the odds are better for everyone.
We are talking about an all-infecting pandemic. You can certainly weaponize it, if you think global collapse sounds fun. What you can't do is target it.
This sort of rhetoric is disgusting, and likely the exact sort that will lead to mass death incidents in our lifetime. I hope you think about that when such comes to pass.
Also, there are numerous examples throughout history of people performing evil human studies; so while people may not have studied children falling from planes, people have studied equivalent things.