Ten years old and "grime-faced," Winfield is the baby of the Joad family, and he's a "trifle of a snot-nose, a little of a brooder back of the barn, and an inveterate collector and smoker of snipes" (10.46). Winfield (along with his sister, Ruthie) adapts more easily to the road trip lifestyle as his family moves westward to California.
That's not to say that he doesn't get shaken. When a family dog is run over on the first day, Winfield takes a long look at the bloody corpse, and then throws up out the side of the family car. Later on, he has to work alongside his family, picking peaches and cotton. At one point, he gets skitters (or diarrhea) from eating too many peaches and becomes very sick. The moral of this story? Don't eat way too many peaches, guys.