Question

Would it be possible to write an iOS app that could prevent other apps from running on an unjailbroken iphone / ipad?

This would be for legitimate purposes, e.g. I turn the app on, hand my iPad to my child and I don’t have to worry that they’ll delete my photos or browse the web.

Answer 1

No, Not programmatically. You cannot control another app from your app unless the iPhone is jail broken. However you can get a list of processes in iOS as mentioned in this post. You can try to send SIGKILL to terminate them if you are not planning to release this app to appstore(Not recommended).

e.g. I turn the app on, hand my iPad to my child and I don’t have to
worry that they’ll delete my photos or browse the web.

Regarding the above point, probably the easiest solution is to check Guided Access for this purpose.

Use Guided Access to:

• Temporarily restrict your iOS device to a particular app
• Disable areas of the screen that aren’t relevant to a task, or areas
  where an accidental gesture might cause a distraction
• Disable the hardware buttons

You can tap Settings > General > Accessibility > Guided Access to set up Guided Access. From there you can:

• Turn Guided Access on or off
• Set a passcode that controls the use of Guided Access and prevents someone from leaving an active session
• Set whether the device can go to sleep during a session

Start a Guided Access session

• Open the app you want to run.
• Triple-click the Home button.
• Adjust settings for the session, then click Start.

Disable app controls and areas of the app screen

• Circle any part of the screen you want to disable.
• Use the handles to adjust the area.

Ignore all screen touches

• Turn off Touch.

Keep iPhone, iPad, or iPod touch from switching from portrait to landscape or from responding to any other motions

• Turn off Motion.

End a Guided Access session

• Triple-click the Home button.
• Enter the Guided Access passcode.

All these details are taken from the above link.