Just William was the first of about 38 books featuring the young boy William, and his gang The Outlaws, the children of the town and their parents.
Despite children being the main characters and adults being a supporting cast, the books themselves were written for an adult audience.
The humor in the series is presented in many levels. If a child reads the books they will be entertained. An adult reader will be able to grasp the adult humor. By adult humor I mean chuckles which a mature mind will readily laugh at.
For anyone who wants a laugh with class, that will stay with you for a long time, I highly recommend the William series.