Trivia: SPOILER WARNING. The character of Kevin was originally intended to be in the film "Unbreakable" (to which this film is revealed to be a sort-of sequel in the final twist scene), but he was removed for thematic reasons, as it was felt that his presence took away focus from that film's true villain "Mr. Glass." Writer/Director M. Night Shyamalan has stated his intentions to make a third film in the "trilogy" that will feature Bruce Willis' character David Dunn from "Unbreakable" being forced to confront Kevin, who will be his ultimate "supervillain."
Trivia: Spoilers. Kevin is seen wearing a purple sweater in one scene, while Dr. Fletcher at one point wears a green scarf and Casey has a green undershirt on in the final sequence. This is a very subtle allusion to the film "Unbreakable", to which this serves as a spin-off/sequel. In that film, the villainous character "Mr. Glass" often wears purple, while the hero of the film, David Dunn, wears green in a number of scenes. Hence, this film's villain is also depicted wearing purple, while its heroes wear green. Director M. Night Shyamalan often uses colors to subtly allude to themes, moods or character motivations in his films.
Trivia: In "Unbreakable", David Dunn survives a train crash and at one point he uses his power and senses an abusive mother who mistreats her child. And in "Split" it is revealed that Kevin's father left him on a train and he was forced to stay with his abusive mother after. Many have speculated that the same train-crash David Dunn survived killed Kevin's father and that the abusive mother David senses is Kevin's own mother. It is possible, as director M. Night Shyamalan has mentioned that Kevin is supposed to be in his mid-20's in "Split", and has been working at the Zoo for ten years... so it is conceivable he got his job in his mid-to-late teens and has been working there ever since.