Does Ooka Island use a continuous narrative?
Ooka Island books use conversational language so that children understand that reading is simply conversation in print. Recurring characters that use conversational language and share everyday experiences draw children into their world which allows them to more easily break into reading.
The familiarity of the characters and situations takes away unnecessary complexity that having to deal with new names and very different environments adds. This allows the child to focus more on the language in print and the reading process.