Wimzie's brother Bo is an 18-month-old baby who looks more like Rousso than Graziella. He is the embodiment of innocence and naiveté, is sociable, curious and pleasant.

Bo is, however, a bit of a loose cannon. As much as Wimzie is eager and enthusiastic, Bo is over the top. His verbal skills consist of pointing at objects and calling out their names with great glee and pride. He is most frustrated when he sees a new object and doesn't know what it is called.

Bo can obviously be a great nuisance to Wimzie, as are most younger siblings from time to time. Horace feels close to him and loves to take care of him.