I grew up in Western North Carolina seeing plenty of mushrooms around the yard, picked them to be umbrellas for my dolls, and peeked under a few, hoping to find a garden fairy. I haven't seen many ...
The mushrooms are probably one of the many kinds of harmless fungi that live in organic matter within or underneath the lawn.
The site recommends spreading a layer of gravel around plants to help prevent mushroom growth, as it blocks out their light.