Continuity mistake: When Cy sneaks into the house with the key under the mat, in the bedroom he picks up the triple gold frame with two photos of Matt with Lyla and one photo of young Lyla in the blue dress in the center frame, then he holds it to his face and places it back on the right side of the dresser. However, after Cy hears Lyla coming into the house, when she sees the underwear on the bedroom floor the frame on the right side of the dresser is now a double wood frame with only one of the same photos seen earlier.
Continuity mistake: The clock on the bomb's secondary timer doesn't match with reality while Prentiss is trying to defuse it - going from 15 seconds to 10 too slowly, then skipping the final few seconds so it can end on 1 second remaining.
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