Brett, his sister Kaitlyn Jane Baumgardner, and his brother Bjorn James Baumgardner were last seen in West Chicago, Illinois on October 18, 2006. They have never been heard from again. They are believed to been abducted by their non-custodial mother. Photographs and information about the mother are unavailable.

Photographs of Kaitlyn and Bjorn are unavailable. Bjorn's date of birth is September 9, 1989; he was seventeen years old at the time of his disappearance. He is described as 5'10 and 140 pounds, with red hair and blue eyes. He has facial freckles and wears eyeglasses or contact lenses. Kaitlyn's date of birth is April 3, 1991; she was fifteen years old at the time of her disappearance. She is described as 5'4 and 125 pounds, with light brown hair and blue eyes. She has pierced ears and her nickname is Katie.

The Baumgardner children's whereabouts are unknown and their cases remain unsolved.