The central conflicts in Tales of a Fourth Grade Nothing are caused by Peter's rambunctious and disobedient younger brother, Fudge. During the course of the story, Fudge is responsible for a remarkable number of unfortunate incidents in Peter's life, all of which lead to conflict within the family.
The list of conflicts between Peter and Fudge is long, and a particularly memorable incident can be found in chapter 7, when Fudge destroys a school project that Peter and two of his classmates have been working on. As usual, this ultimately becomes a conflict between Peter and his mother, because he yells at her for failing to keep Fudge out of his possessions.
Earlier, in chapter 3, Fudge refuses to eat for a few days, and this causes conflict between Peter and his mother when Peter shows reluctance to stand on his head to get Fudge to eat and states that his brother will "eat when he gets hungry." Once again, Peter is up against her mother's blind love for her brother and the fact that Fudge can get away with anything.
Ultimately, the central characters in this novel are up against the force of nature that is Fudge. His disobedient nature causes endless conflicts and trouble for members of his family and those who visit the family's apartment.