To quit the reactable mobile in iOS you can do one of two things:
1.- Go to setup tab->settings, and deselect the background audio setting (it is on by default). When you press the home button it will stop the audio playing on the device and keep the app minimized.
2. If you want to keep the audio in background setting on but close the application use the normal procedure to shut down iOS apps. More details can be found here:
Hope this helps.