Sorry you were having issues. These are the steps to take to make sure the lessons have sound on iPad.
Adding to this for more tips...
Also, if you open your 'control center', can you please click and verify that mute isn't turned on? To access control center, swipe your finger up from the bottom of the screen and then click the icon that looks like a bell.
Here's an article about how the ipad side switch works. It can control muting audio or locking screen rotation, and we have had other users that have inadvertently muted their audio with the switch:http://support.apple.com/en-us/HT4085
Please let us know if any of these fixes the issue for you.
If you have any questions, comments, or concerns, please contact us