Willie lived in Walnut Grove in his family's store. Mischievous and spoiled as a child, Willie causes trouble and plays pranks on other children including his own older sister Nellie. Like with Nellie, Willie was rarely punished being prevented from being so by his mother save for when her image or some precious object of hers was damaged or destroyed. (Episode 806: Gambini the Great) He was sometimes a peeping tom; sometimes he would look through the woman's underwear catalogue, but only when his mother wasn't around. He even tried to watch Laura while she was changing her clothes, but only once. It appears that, as a child and in his early teens, Willie had a soft spot for candy and would often try to take candy from his family's store.
He had a ravenous appetite for food and was often known to go along with his sister's schemes in exchange for food. (Episode 305: The Monster of Walnut Grove) He was often seen stealing food from peoples' plates like he did with his father when Harriet was out of the house, after leaving over the women's rights petition. His father could never understand where he puts all the food that he eats. (Episode 712: Oleson Versus Oleson) He was seen experimenting with food when he is seen making a ridiculously overblown sandwich while his parents were out. (Episode 801: The Reincarnation of Nellie (Part 1) His appetite foiled Nancy's plan to use a liquorice shaped revolver to hold up the Walnut Grove Bank to get the ransom money when a pair of kidnappers abducted their parents, when he simply ate it because he got hungry while waiting. (Episode 807: The Legend of Black Jake) He, along with the other Olesons and the Garveys and Ingalls, move and stay in Winoka for a time. Nels and Harriet are the only family who are able to afford and send their children to the Winoka School, which Willie hates because he doesn’t like the tie on the uniform and wishes he could go to school with Laura, which Nellie despises.
Willie has a hard time trying to make friends and often had to bribe and barter with the other kids to even get them to talk to him properly. Once some of his so called "friends" tried to get him to steal cigars from his family store. Carl Edwards, one of the kids he bartered with who never liked him and once got him into trouble when he traded him some leftover fireworks for some aggies. (Episode 216: The Runaway Caboose) These schemes always got him into trouble. And Nellie sometimes bribes him to help her with her schemes, as when Nellie gives Willie a smoke pipe to tell everyone to vote for her. But Willie ends up voting for Elmer Dobkins because Nellie keeps picking on him and Elmer won’t let her. (Episode 320: The Election)
Most of the time he gets into fights and trouble with Laura Ingalls. If they play marbles and Laura won, he would refuse to hand over his marbles and argue with her until Miss Beadle came along. He often abused the Ingalls children and kicked Laura on one or more occasions. (Episode 122: Money Crop) and once bit Mary. (Episode 120: Plague)
Although Willie was very mischievous and sometimes mean, on rare occasions Willie can be nice when he is seen comforting the saddened and guilt-ridden Miss Beadle, during a devastating blizzard. (Episode 311: Blizzard) It is at school that Willie often gets into trouble; he is always being sent into the corner for his behavior by his teachers Miss Beadle, Mrs. Garvey, Mrs. Eliza Jane Wilder, and Mrs. Laura Wilder.
Willie later matured into a responsible young man after Laura becomes his teacher. His major change in attitude came after Laura had collapsed in the field from a heat stroke from overwork, due to Almanzo's absence. Willie demonstrated genuine responsibly in immediately fetching Doctor Baker, which saved her life. Caroline later told him the story Stone Soup. Understanding the moral of the story, he and his classmates filled buckets of water to help irrigate Laura's crop. (Episode 813: Stone Soup) Afterwards, he abandoned his old ways and started behaving properly and respectfully.