Only a few kids are dead. That's because they gave them a sleeping medication, maybe fentanyl. Because they are amateurs, and they do not understand how different people respond differently to the same quantity of a drug, they killed some of the kids. There is some video with an older boy having a hose run over his head, and a baby held face down being slapped on the back. The whole scene is suspiciously like trying to reawaken someone who took a sleeping pill and is not waking up when they should.
As you pointed out, one of the babies does have purpling of the ear indicating that it is dead. However this does not mean there was a real chemical attack. There have been numerous White Helmets videos so those of us who are familiar with their work know that they are sloppy, and complete amateurs when it comes to paramedics. They probably chose fighters who look pretty and they call them in for a couple of days special duty every once in a while. That's the only way I can explain their gross incompetence in first aid technique.
In one film I saw I am sure they used dead children. That was around the time Aleppo was falling and they were shooting people who tried to escape. Probably they collected some orphans and killed them to make movies. It would be interesting to get real emergency physicians to examine the film that won the Oscar because it may actually be a snuff film. If so, The Academy should be strongly censured, if not shut down entirely.