Joseph, you are falling to a new low this time. A letter is talking about dinei nifashos, and you choose to focus on which parent should write the letter, who it should be addressed to, and whether the school is required to handle it.
I repeat: this is DINEI NIFASHOS. A child being bullied in school can have long-term effects. I DON”T CARE WHICH PARENT WRITES THE LETTER!!! Joseph, you are the very definition of a chossid shoteh. I really don’t know why the mods still tolerate you – if it were up to me, I would have banned you a long time ago.
Whether the local laws require reporting or not shouldn’t matter. The school has a halachic responsibility to act on it. End of story.