The Adventurous Four series does not have a new book coming out soon. The latest book, Off with the Adventurous Four // Trapped! (Book 3), was published in January 1952.
The first book in The Adventurous Four series, The Adventurous Four, was published in January 1941.
The Adventurous Four series primarily falls into the Action Adventure genre. This middle grade series was written for ages 8-12, but can be enjoyed by older readers as well.