In my experience, cards are discouraged, but generally accepted. I’m aware they don’t like seeing them but I’ve never had any complaints when I’ve used them. For u11, I’d be incredibly surprised if you needed cards at an academy game unless it’s a unique incident. My academy games with the younger ages tend to be fairly easy and the players are pretty innocent or at least easy to manage. U14 and up seems to be where games get a bit more feisty in my experience