How to fix sound
I have a new iPad mini 2, encountered the sound issue, and was able to resolve by turning the iPad ringer volume on. Seems like this app uses the ringer/alerts sound settings, rather than the normal audio sound settings. On my iPad, the way to unmute is to use your finger to flip the switch on the side of the iPad next to the audio controls from mute (red dot showing) to unmute (no red dot showing).
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Peppa Pig: Holiday, v1.1.2