Continuity mistake: When Rossi is in Zoe's bedroom the camera pans the room and we see the laptop on the desk with nothing on its lid, but in the closeup suddenly there's a large embroidered flower sticker on the laptop's lid, which vanishes again when Rossi lifts the lid.
Continuity mistake: There's a clock on the first victim's night stand. When she goes to bed, it's Tuesday, 11:06. When the murder happens a couple of hours later, it's still Tuesday, 1:13.
Continuity mistake: When Reid is talking there's a big crack at the top of the window that might be a problem since they're supposed to be flying. Then a few seconds later they cut back to him and it's filled with putty. (00:05:00 - 00:06:00)
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