Depending on whether the app was developed specifically for Android or ported from a different platform, the steps to exit the app will be different.
The Pet Play World app exits in the standard Android way. Swipe up from the bottom of the screen to reveal the "Exit" icon, then tap the Exit icon to exit to the Home screen.
The Stretchy Monkey 2 app is an app that was originally designed for a different platform. To exit, this app requires the user to tap the Pause button, tap on Quit, then tap the Home icon to exit to the Home screen.
Note: Pressing the power button will also exit an app, however this is not recommended. Exiting an app by pressing the power button will not save game progress or your child's learning progress.