Based on his appearance, Sadie and Carter don't know what they're getting into with this dude: "He was a tiny man, crudely fashioned, as if the maker had been in a hurry. His arms were crossed over his chest, his mouth was open, and his legs were cut off at the knees" (7.81). As if that's not weird enough, he grows warm to the touch and talks when directly addressed.
Turns out he's a shabti, a magical servant created by Julius Kane. He's also a smart-mouthed pain in the butt, but that's neither here nor there. While he's only supposed to answer to Julius, the kids are able to give him orders and make him do stuff. So while Doughboy is prone to complaining about his lot in life, he's pretty useful in the end.