How does "power of attorney" have any relevance here?
The argument is simply that the school district has suffered damages from specific behavior by the social media companies, that has nothing to with an ability to make decisions on the student's behalf.
Having read the complaint, no, it doesn't have relevance here (obviously I made that claim prior to reading the complaint), but what they do assert is even worse: They're trying to claim that use of Facebook, Tiktok, etc and consequent behavioral issues among students constitutes a nuisance. The phrase "void for vagueness" would seem to apply here.
It wasn't, actually. I made that comment before I read the complaint. The statutory basis of their complaint is that Facebook constitutes some specie of nuisance, hence my later comment that even if we took their factual assertions at face value the charge asserted should be void for vagueness.