About Face - S3-E6
Continuity mistake: Senior SSA David Rossi is clean-shaven in the beginning and middle of the episode. Toward the end of the episode, which takes place over mere days, he has magically grown a full mustache and beard which disappears and reappears in the last scenes.
About Face - S3-E6
Continuity mistake: This episode is a flash back to when Agent Gideon joins the team, but agent Prentiss is already a member. She didn't join until season 2 (when agent Gideon was already an established character).
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 his 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