I got curious about this the minute you asked — the title 'The Little Mushroom' (or whatever variation it appears as) isn't one of those guaranteed-audio household names, so whether there's an audiobook depends a lot on who published it and when. If it's traditionally published, the easiest places to check are Audible, Apple Books, and Kobo; those platforms host the bulk of commercial audiobooks. For library access, Libby/OverDrive is my go-to — I once found a whole indie fantasy I missed because my library had the audiobook and the ebook but not the paperback.
If the book is self-published or a smaller press, chances are lower but not impossible: some indie authors produce their own narrations or hire narrators via ACX, Findaway, or local freelancers. If you can't find any listing, try searching the author’s name plus the word 'audiobook', check the publisher’s site and the author’s social accounts, and peek at Patreon or Kickstarter pages — creators sometimes crowdfund audio productions. If all else fails, grab the ebook and use a quality text-to-speech app like Voice Dream Reader or NaturalReader; not the same as a professional narration, but surprisingly comfy for bedtime listening.
If you want, tell me the author's name or a link and I’ll help dig up specifics — I'm always happy to hunt for hidden narrations and fan uploads, and I love comparing narration styles when I find them.