So what you're thinking of is a solution to have an iPad only have one app open and have that app be the only thing displayed when the device is unlocked.
I have been jailbreaking iDevices for years, and I've never seen the option of having to enter a password to exit an app or return to the home screen, however the closest thing I can think of would be to get the NoLockScreen tweak so that when you do unlock your iPad it goes right to that app, as long as you never touch the home button while the iPad is unlocked.