Continuity mistake: At the start of this episode Rossi tells Garcia about the case he's obsessed with, "It's the 20th anniversary of this crime. Twenty years tomorrow, three children woke up and found their parents murdered." However, during S3xE11 "Birthright," while working on their current Wilkinson case, Rossi shows Caulfield (the sheriff of the original Wilkinson case from 1980) the victim's charm bracelet he carries, then tells him about the Indianapolis case he's never forgotten, and how every year since then he's called the victims' children. And later, after Caulfield tells Rossi it's been 27 years since his own unsolved case, he asks Rossi how long it's been for him and Rossi says, "21," then Caulfield cautions, "Don't let it get to 22."
Continuity mistake: When Rossi is telling Prentiss, Morgan, and JJ about the original Galen case, he says that the Galen parents were butchered with an axe, but in "Birthright", he tells Detective Caulfield that they were beaten to death.
Answer: "The Boogeyman", s02e06. Spoiler alert: The kid is Jeffrey Charles and at that point he had already killed 3 other kids. Jefferey basically hated and resented other kids after his mother abandoned him and his father spent a lot of time with other children because of her job. Jeffery would lure kids Into the Woods and then beat them to death with his bat just because of hate, no particular "reason." The scene you're describing, Jefferey agrees to walk Tracy home when her "buddy" leaves her (at this point the FBI announced there's a serial killer on the loose and kids should walk with a buddy). Jeffrey gets mad at Tracy for walking too slow and for complaining, and he takes a swing at her, causing her to flee Into the Woods and have Jeffery chase her.
Bishop73