Along with several hundred other people, including many young children, I spent a big chunk of five days on a big ol’ ship — one of many on the high seas. On this big ol’ ship I found a library stocked with scores of hardback novels for adults but not a single picture book. I’m betting that the situation’s the same on other such ships.
Ahoy there, marketing departments at children’s publishers: I don’t know how you define “captive audience,” but I think I’ve found one for you. Don’t miss the boat.