Ever since my niece latched onto it, I've been fielding 'again, again!' for the fifteenth read-through of 'The Very Hungry Caterpillar'. That's the sweet spot—it's pure toddler fuel. The holes in the pages are a tactile playground for little fingers, the counting is simple, and the colorful food gets big reactions.
The caterpillar's transformation feels almost magical to a 3-year-old, but the short sentences and repetition are perfect for the 'I can read it myself!' phase right after. Once kids are asking more complex 'why' questions or wanting longer narratives, they tend to move on. It sits firmly in that 2-5 range, a total preschool classic. I'd argue a one-year-old might just try to eat it, which, honestly, is thematically appropriate.