<P> Dr. Jason Seaver ( portrayed by Alan Thicke ) , a psychiatrist , works from home because his wife , Maggie ( Joanna Kerns ) , has gone back to work as a reporter . Jason has to take care of the kids : ladies ' man Mike ( Kirk Cameron ) , bookish honors student Carol ( Tracey Gold ) , and rambunctious Ben ( Jeremy Miller ) . A fourth child , Chrissy Seaver ( twins Kelsey and Kirsten Dohring ; Ashley Johnson ) , is born in October 1988 . In the middle of season four ( 1988 -- 89 ) , she was first played in her infant stage by an uncredited set of twin sisters . Then , by season five ( 1989 -- 90 ) , she was played in her toddler stage by alternating twins Kristen and Kelsey Dohering . In seasons six and seven ( 1990 -- 92 ) , Chrissy 's age was advanced to six years old . By the seventh and final season , homeless teen Luke Brower ( Leonardo DiCaprio ) is brought into the Seaver family to live with them until nearly the end of season seven . </P>
who played the part of the homeless person who came to live with siblings mike carol ben and chrissy
Leonardo DiCaprio