If any school district cares, all the kids will essentially end up repeating a grade. This is not the end of the world. If anything, it might improve student achievement. (Students who are born right after the cutoff for a particular elementary school class, in aggregate, outperform the ones born just before, the youngest in the class.)
Outside of college-bound seniors — a special case — the main price is their time, same as anyone else, and their caregivers' time.
2) the count of districts ready to have a 7.7% student headcount increase in one year (you're doing this for 13 grades at once, plus have another coming in) on top of whatever growth they already expected approaches zero. I mean, hell, think of what that would do to the teacher labor market alone if even 10% of districts all did that, putting aside things like building space and bussing.
It sounds more like you haven't thought this through.
voted +1 touché
I don't know if they'll be roaming the streets (the police in America are pretty unforgiving), but I can certainly say they will have it worse than ~2001 and ~2008 graduates.
But kids in poor home situations who were already barely scraping by--if that--will basically lose the year and everything that implies. In some areas, double-digit percentages of students have basically gone incommunicado from their schools.