Here's another bilingual reader we picked up a few months ago. I've read The Napping House to countless preschoolers over the years, and when we decided to teach nuestra hija Spanish, the decision was obvio. Like La Oruga Muy Hambrienta, La Casa Adormecida is definitely kid-approved and a classic.
The story details a family of people and animals co-sleeping until awoken by a flea (ouch!). The book has a very cozy, reassuring feel, and the repetition makes it easy to learn new words and phrasing in both Spanish and English. You also learn lots of synonyms for napping, dozing, resting, and so on.
La Casa Adormecida is very affordably priced at around $5 at Amazon and will most likely be available for free at your local library in some form.