The Willoughbys by Lois Lowry

The Willoughby children—Timothy, twins Barnaby A and Barnaby B, and their sister Jane—are fond all old-fashioned things, but especially old-fashioned adventures. What they aren’t fond of, however, are their parents. Truth be told, their parents aren’t the fondest of them, either, and they’re concocting an evil plan to get rid of their children once and for all!

Both parents and children have plenty of dastardly ideas and tricks up their sleeves. The only thing they don’t have is any idea of what lies between them and a happily-ever-after.