When creating a mobile game, pretty much all of your interactions are controlled by button and screen taps. Buttons that are a reasonable size on a PC or console game may be too small for a mobile game.
Apple, Google, and Microsoft all have specific recommendations for the size of a button's touchable area when designing for their devices: Apple recommends that buttons be 44 points x 44 points; Google recommends 48 dp x 48 dp with 8 dp spacing between two more buttons; and Microsoft recommends 9 mm x 9 mm with 2 mm padding between two buttons. Annoyingly, all of these recommendations are in different units of measurement.
You can find information about designing touch/hit areas for each mobile platform at the following locations:
