What makes an iPad home screen "go big"? its like the screen has been pinched outwards

What would make an iPad screen "go big"? My son keeps experiencing an issue where the home screen will enlarge and freeze. I am unable to replicate this on any of our other apple products (iPhones and another iPad). Is it possible that he is pushing or clicking something that I dont know about? If so, what would that be? Is there somewhere in the settings menu that I could keep this from happening for him? Any advice or answers help. Thank you.