In December 2003, Welling made his feature film debut as Charlie Baker, the oldest son and second-oldest in the Baker family which had 12 children, in the family comedy "Cheaper by the Dozen" with Steve Martin and Bonnie Hunt, which is a remake of the 1950 movie starring Clifton Webb and Myrna Loy, based on the 1948 book about the family of Frank and Lillian Gilbreth and written by two of their children. Welling talked about why he was interested in the project in an interview with Paul Fischer: "The top three reasons I decided to do this film were, one, Steve Martin, two, Steve Martin and three, Steve Martin. That was the number one draw for me. Then, after reading the script, I really liked this character, Charlie. I liked what he went through, what he had to go through, and I felt I understood where he was coming from. And I just wanted to be a part of it." Welling had always been a fan of Martin's and said that he "absolutely loved" working with him.