It’s possible that the ban on the US flag is the consequence of the decisions necessary to ban the rainbow flag, the Mexican flag, etc.
Can’t really blame the school/school district here. There’s several decades of legal precedent going a the way up to Supreme Court cases that insist on all or nothing policies when it comes to public displays of things like flags.
The kids should put the flags on the inside windows of the cars next 9/11.
I doubt that rainbow flags or Mexican flags are banned