Should a Children’s Book Cover Show the Main Character’s Face or Leave It Hidden?

I am working on a picture book for 3 to 6-year-old readers, but I am not sure whether to put the front view of the central character on the cover or whether to keep the character’s identity mysterious by using a rear view, silhouette, or miniature image. As I explore childrens book cover design Toronto alternatives, I would appreciate hearing how things worked for others in this area. Is it preferable to use the front view of a character to attract readers’ attention, or is it better to create a mysterious cover that will make children and their parents want to learn more about the book? Does your choice depend on the format – board books, picture books, or early chapter books? Has anyone tried using two covers and can share the results?