However the tone implied a “know-it-all-it’s-easy-just-do-this” solution, which, as everybody who has had children knows, does not exist. Every child is different, and they all respond differently to the same thing.

Furthermore the comment gave explicit orders and judgments of other parents, which, if he is not a parent himself, is completely unacceptable (and even if he is, it is still unacceptable). The rule is simple: never ever judge a parent. You do not know the sh*t they have to deal with (and tbh the same goes for non-parents too…).

Obviously giving advice is completely fair, but the tone matters.