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.
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."