Actually, I believe there are federal statutes that prevent the Mexican flag from being flown over govt property. Someone posted them on another thread tonight. If I were the kid's family, I would be making sure that the original flag thugs had appropriate charges filed against them.
Forbidden flags
The U.S. has no such prohibitions, but 17 states do have "forbidden flags."
California
prohibits the display of the "red flag or any other flag in a public place" as a sign of violent opposition to organized government. No state military group may carry other than the U.S. or State flags.
1919 California Penal Code, § 403a: "Any person who displays a red flag, banner or badge or any flag, badge, banner, or device of any color or form whatever in any public place or in any meeting place or public assembly, or from or on any house, building or window as a sign, symbol or emblem of opposition to organized government or as an invitation or stimulus to anarchistic action or as an aid to propaganda that is of a seditious character is guilty of a felony."