Step 1: For Android it may be different from phone to phone but in general there are only two methods. Press the menu button on the left or the right, one of them is Back and the other opens a window with all the applications running at that time. From there you can close all of them or just what is needed.
Step 2: Click on Close All or Close Applications and all applications will close.
If you only want to close the Kinderpedia application you will have to "slide" it up or down. (depends on the phone).
For IOS the steps are as follows:
Double-clicking on the "Home" button opens a window where you can see all the applications open at the moment of contempt. And from here we "slide" the Kinderpedia application up or down.