The only child of medical professionals from Northern California, Oleynik broke into show business at age eight when she survived a cattle call audition and won the role of young Cosette in the San Francisco production of "Les Miserables". During the year-long run, the youngster showed her dedication by taking acting lessons and later proved how serious she was by landing roles in a 1993 episode of "Dr. Quinn, Medicine Woman" and as the daughter of a divorced mother terrorized by a drug dealer while on a rafting trip in "River of Rage," (CBS, 1993). She won the role of Alex Mack over 400 other aspirants. Oleynik segued to the big screen, providing the voice of the young Odette for the animated "The Swan Princess" (1994) and made a memorable acting debut as the environmentalist Dawn in "The Babysitters' Club" (1995), Oleynik also guested starred on two 1996 episodes of "Boy Meets World" (ABC), playing a girlfriend to Shawn (Rider Strong, who also appeared in the San Francisco production of "Les Miserables"), though she at first, would rather pair with the more stable Cory (Ben Savage). Oleynik's popularity with "tweens" led to an advice column published in TIGER BEAT magazine.