It’s definitely not a no-no to split up a chapter. Go right ahead. This might be a great opportunity to practice short lessons. Set the timer (or just make a mental note of what time to quit), read in short passages, have them narrate as you go, and end after 15 or 20 minutes.
As time goes on, and they get more skilled at listening and narrating, you might extend your reading to two paragraphs before they narrate, then maybe three, then maybe a page or two. But if you call it quits after 15 or 20 minutes — before they have a chance to lose attention and motivation — you’ll be training them in the habit of paying attention for the whole lesson. Then next year you can extend that lesson time to 20 or 30 minutes, plus you’ll be covering more material at a faster pace because they will be able to listen to more paragraphs before stopping to narrate.
It’s a process, and as Jill pointed out, using a book that captures their imagination will definitely help the process! 🙂