Continuity mistake: After Garcia traces the phone call, Morgan and Rossi are shown driving to the area of the cell tower. When the shot is from outside the car, the car is a 10th generation (07-14) Chevy Suburban. When the shot changes to inside the car, it's an 11th gen (15-16).
Continuity mistake: After Emily shoots the unsub in the head and he falls on the bed, the gun falls beside him. A second later they show her walking over to his body to remove the gun from his hand. (00:51:00)
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