Balthazar

Balthazar is a small boy who's part of Master Payne's Circus of Adventure. He's very important to plot development, as Agatha's first contact with the Circus comes when she finds him lost and up a tree, and delivers him to his mom, Trish Belloptrix. They and the other Circus people take a liking to her (and Krosp, who's involved in the discovery but isn't sure whether they should rescue the kid or eat him -- eeuuwww!) and feed her a meal, setting in play all manner of merry adventures.

He plays the role of general camp gofer, for example taking Smilin' Stev out to collect firewood. This too is important to plot development, as Agatha's close inspection of Stev is her first hint that there may be more to the Circus than meets the eye. Another contribution he makes to the plot is donation of a moderately cool coat that he's outgrown to Krosp.