I'm guessing the claim is that saying "Israel is killing children" present a "false" narrative (presumably, false to them). Like you can imagine someone saying "Stop this man from killing puppies!" and it makes him look pretty bad even if he's not a puppy killer.
What's unfortunate is that instead of responding to "false" narratives by pointing out the falsehoods ("Actually all those bombed children's hospitals were faked!" /s), instead this person just attacks the character of the person saying it. It's basically name-calling or tone policing at best. I'm guessing because there's no good argument in support of Netanyahu's actions. Only zealots would support him.
They are killing children, it's not a false narrative, it's what's happening. Palestine has a very young population, those casualties contain a very large percentage of underage people. They don't have to bomb a children's hospital to kill children.