Other mistake: At the start, it's nighttime when the unsub hides in the house of the soon-to-be victim who goes to sleep when her alarm clock reads 'Tue 11:06', and then we see the time morph to 'Tue 1:13' when the victim is sound asleep, before the unsub comes out of the closet to kill her. However, the time on the clock should actually read 'Wed 1:13'.
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.
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