Every book on this shelf is Spanish and English. That's the first thing to say, because 'bilingual book' on its own tells you nothing, and this shelf is Spanish — if you came looking for Mandarin, Korean, or Arabic, they aren't here yet. The second thing to say is that these six books are bilingual in completely different ways, and the difference is the entire reason to read this page. One of them prints the whole story in both languages on every page. Four of them are English stories with Spanish words woven in. One hides its Spanish in the labels on the pictures. Those are different products for different families, so each note below tells you which kind you're holding. Pick one and give just the one that fits.
You pick the one that suits the family and you're done. What makes the choosing hard is that 'bilingual' gets printed on the cover of books that work in completely different ways, so here's the map. 'Book Fiesta!' is the only dual-text one: the full story in English and the full story in Spanish on every single spread, which means a Spanish-speaking abuela and an English-speaking parent can each read your child the whole book. 'Marta! Big & Small', 'La Madre Goose', 'Federico and the Wolf' and 'Mango, Abuela, and Me' are English stories with Spanish woven in — the Spanish word arrives inside an English sentence that hands you the meaning a beat later, so you learn by absorption and a Spanish-only reader would find little to read. '¡Vamos! Let's Go to the Market' does something else again: the story is English, but the market in the pictures is labeled in Spanish top to bottom, so the words come from the artwork. Every one of these is in Latin script, so there's no alphabet to learn and no romanisation needed; three of them ('Marta!', 'La Madre Goose', '¡Vamos!') carry a glossary at the back, and 'La Madre Goose' is the only one that also tells you how to pronounce each word, which matters if you're reading aloud in a language you don't speak. One more thing worth knowing: 'Mango, Abuela, and Me' has a full Spanish edition, 'Mango, Abuela y yo', sold as a separate book. If the gift is for a Spanish-reading household, that's the one to buy instead.