If an app shuts down by itself it is an indication that you are using all of your iPad's RAM and it is struggling to manage the memory effectively. The best solution is to ensure you have fully closed (not just backgrounded) all apps which you are not currently using.
To do this, double tap the home button so that the switcher bar appears at the bottom of the screen. Then hold any one of the icons until they all start to wiggle. Now press the "X" on each icon to fully close it and remove it from memory.
Once the list is clear you should find that the apps you are using will not shut themselves down. Whilst IOS has very good memory management, when too many things are in the background it can struggle to manage memory effectively, so it is worth clearing out the apps from the switcher from time to time if this starts to happen.
Hope that helps.