Follow the directions below to make sure the sound is turned on in Disney Princess Palace Pets:

1. Tap the "i" icon in the upper left-hand corner of the screen
2. Enter the security code.
3. Tap the "Help" tab at the bottom of the screen.
4. Make sure that "Music" and "Narration" are both set to ON.

If this doesn't help, please check your device settings to see if the sound has been muted.