If you are puttering with your iPad, and its sound suddenly stops working, you can try a few things to restore the sound. Make sure that
You haven’t touched the volume-control keys on a physical keyboard connected to your iPad via Bluetooth. They’re on the right side of the top row. Be sure not to touch one and inadvertently mute the sound.
You haven’t flipped the Side Switch. If you have the Side Switch set up for the Silent feature, moving the switch mutes sound on the iPad.
The speaker isn’t covered up. It may be covered in a way that muffles the sound.
A headset isn’t plugged in. Sound won’t play over the speaker and the headset at the same time.
The volume limit is set to Off. You can set up the volume limit in the Music settings to control how loudly your music can play (which is useful if you have teenagers around). Tap the Settings icon on the Home screen; then tap Music on the left side, tap the Volume Limit control, and move the slider to adjust the volume limit.
When all else fails, reboot. (This strategy worked for us.) Just press the Sleep/Wake button until the red slider appears; then press and drag the slider to the right. After the iPad turns off, press the Sleep/Wake button again until the Apple logo appears, and you may find yourself back in business, sound-wise.