The techniques go from simple line drawing, like Dav Pilkey in the earliest Captain Underpants books, to the architectural illustrations of David Macaulay (Pyramid, or Cathedral, or Underground), to the achromatic Conte crayon of Chris Van Allsburg (Jumanji, The Mysterious Garden of Abdul Gasazi).
In many older children's books, black & white illustration was used throughout the pages of a book because of the technical limits of the publishing process at the time, and the expense of publishing in color. Beverly Cleary's work is an example of that. as well as Ernest Shephard, who illustrated A. A. Milne's Winnie the Pooh books.
Link to Analysis of Illustrations in Jumanji: https://www.slideshare.net/Trabolin/jumanji-book-slide