These are bird’s nest fungi (probably a Cyathus species), which like to grow on wood. They look like they have tiny eggs inside their cups. They start out as little goblet shapes, then open up to reveal the “eggs” when the rains start. Raindrops falling into the cup splash the “eggs” out some distance away from the nest. If they fall onto suitable wood they will germinate and sprout new mushrooms eventually.
These are growing on our back fence. The cups are no bigger than my fingernail (10 mm).