Recommended audio export settings for iPad app?

I'm new to app development and would like to know what the recommended audio export settings should be for audio that will be used in an iOS app for iPad or iPhone.

I know .mp3 files should be used, but not sure if stereo or mono is best?
Would also like to know what is the recommend volume level one should use because when I plug headphones and listen to the audio on laptop is sounds much louder than when I unplug the headphones and listen off my laptop speakers. My app is for toddlers so maybe I don't need to worry about the louder volume on headphones...

I'm using Garageband to export my audio into .mp3 and importing the audio into Flash and exporting the app as an adobe air app.

Thanks in advance for your thoughts.