Guided Access Settings

Here's how to set the guided access setting...

First, you will need to enable it in the "Settings". Go to "Settings"-->"General" 

You'll need to swipe up (on the right side) to get to the bottom of the list--which is where "Accessibility" is located.

Open 'settings'

Go to 'general'

Swipe up to get to the bottom of the general settings &  select 'accessibility'

 Once in the Accessibility menu, you should see 'guided access' listed under Learning.  It will be "off" by default (mine is "on" in the screenshot because I'd already set it up :) ).  Touch it to open the menu and turn the feature "on".  

It will also open the Guided Access options...

Guided access options

 If you really want to make sure the kids can't get out of the app, set the passcode...just make sure you remember the 4-digit code you enter, or you won't be able to get out of the app either!

Now that you've set up the feature, you can activate it from any app.  To activate it, open the app and triple-click (press 3 times, quickly) the "home" button.

Press the "Home" button (circled in red) 3 times in a row, quickly

 That will open some options...

Guided access options, once activated in an app

When you have selected all the options you want, touch "Start".  You will not be able to exit the app unless you de-activate it by triple-clicking the "home" button again and entering the passcode.