I don't know where you watch your football games, but the Ref
did not inspect, and I have looked at the rules and there is nothing specifying the yellow bracelets (just the generic uniform code) as have being banned this season. This was truly an oversight. I agree it was "illegal", but also insensitive.
I am not saying that we didn't "deserve" the penalty, I was just commenting on the irony of an "unsportsman like" penalty when the kid is just supporting his brother. And the sometimes unwavering "rules are rules".
I am an official with the Northern Ca Officials Assoc. I ref HS games throughout NorCal. We always inspect and warn before games. This is a new rule this season and it may not have hit your book. I don't know what happened in your game, I only know what we do! While it may not seem like a big deal, from plastic bracelets to metal is not a stretch and equipment is regulated to protect the players.