Final answer:
James Patterson likely wrote a different genre before creating a children's novel, and considering the historical context of early children's literature, the most probable type of book he wrote was a Sunday school book.
Step-by-step explanation:
The question seems to ask about famed author James Patterson and the type of children's book he wrote before creating a children's novel. While the question does not provide the clear context needed for a precise answer, based on the information provided and the understanding of children's literature, it would be reasonable to surmise that Patterson may have written a different genre of children's literature.
Children's literature has evolved over time from being purely educational with moral messages to a respected literary genre that includes an array of styles, including fantasy, adventure, and satire. Early literature for children often had a moralistic and Christian motive. Given that the provided options are 'Children's novel', 'Sunday school book', 'Textbook', and 'Poetry book', and considering that 'Children's novel' is excluded by the question itself, the most likely answer of the remaining choices would be a Sunday school book, which fits the historical pattern of early children's literature being used for moral and religious education.