Swimmy is a longtime classroom favorite of mine for its rich descriptive language and unique hand-painted illustrations. If you are unfamiliar with the author, Leo Lionni, it’s worth checking out bud other books.
Ironically, my children first discovered this book through the reading app, @learnwithhomer. I happened to have a copy at home which we’ve been reading as well, but because it’s such a classic, it is also available online in many forms. Link in bio to KCLS ebook and YouTube read aloud.