IPhone 4S: iOS 7, how do I keep apps running in the background?

I like to play fantasica and nfl matchups, but everytime I switch from say fantasica to any other app, or even the home screen, I have to restart the whole app to play it. When I double tap the home button to bring up the background apps that are running, it is still open to what I was doing, but if I open it, it will restart. Can someone please help me?

That is just the way the apps were designed. When it restarts everytime you open it (even if it was running in the BG), it is just trying to load new data to the app (scores, updates, etc.)