Once picture books start to feel short, an animal on the cover is still the easiest way into a chapter book. The child already cares what happens to a pig, a dog, or a gorilla. The chapters can do the rest.
Start with the one they can finish. Charlotte\'s Web and Stuart Little have been read aloud for years because the chapters break cleanly at bedtime. The One and Only Ivan and Pax ask for a little more quiet, so they fit a weekend better than a rushed school night.
Read the first chapter together even if they want to take the book to their room. You will hear whether the words are sticking. If they are guessing every line, drop back to a shorter book and try this pile again in a month.
These are stories with animals in them, not a stack of pet facts. If they want facts after the story, that is a separate book.
When they finish, ask which animal they want next, then stop talking. The next book can wait until tomorrow night.