Why can't I hear any of my games?

Have you got muted notification sounds on your iPad ? That will mute notifications, including games, but the Music and Videos apps, and headphones, will still get sound.

Depending on what you've got Settings > General > Use Side Switch To set to (mute or rotation lock), then you can mute notifications by the switch on the right hand side of the iPad above the volume switch, or via Control Centre : swipe up from the bottom edge of the screen and it's the right-most of the 5 icons in the middle of it (if the icon is white then it's 'on', tap it to turn it grey and 'off'). The function that isn't being controlled via the side switch is controlled via Control Centre instead : iPad: Understanding the side switch.