Joe,
I've sent a player off to get the proper pads; same as I do if a player tells me he can't buckle his chin strap because the snap is broken or missing. I'd also relay a message to the coach that any other infractions will be penalized.
We were also told in a meeting a couple of weeks ago to be prudent in making sure that the knee pads cover the knees. One of the top ranked teams in the state was cited as a team that has players that violate this rule. Interesting, they're last game is being televised on MSG. Let's just say it seems that not all officials got the message.