Mushroom in the Rain by Mirra Ginsburg, illustrated by Jose Aruego and Ariane Dewey / ISBN 9780689714412 / 32-page paperback, 8 x 10 inches, published by Aladdin Books (first published in 1974)
Caught out in the rain, an ant takes shelter under a very tiny mushroom. Soon, a wet butterfly, then a drenched mouse, a dripping sparrow, and even a rain-soaked rabbit each beg to join him under his miniature umbrella. How can the ant let the others in when there is barely room enough for one? But as the rain comes down and down, they all somehow manage to squeeze together and share the tiny shelter. And when the sun finally comes out, the ant discovers a magical secret of just what happens to mushrooms in the rain!