“Small potatoes” is a phrase which has nothing to do with root vegetables that happen to be tiny in size.  Instead, it refers to the change in one’s feelings for something when it is compared to something else.  If you were walking in the rain, for instance, you might be worried about getting wet, but if you turned the corner and saw a pack of vicious dogs, getting wet would suddenly become small potatoes next to getting chased down an alley and barked at, or possible eaten.

A Series of Unfortunate Events: The Vile Village – Lemony Snicket