What he was doing was completely harmless. If he was taking a hammer to it, then that would be a problem.
The point is DON’T mess with other people’s children. It is NOT your responsibility.
Screw your attitude. If you can’t take the time or effort to correct your little punks behaviour in public you can expect me to do so. Then if you have an issue with me telling your undisciplined animal to behave like a human being you can take whatever action you feel is necessary. And so will I.