Watson, who lived in the San Diego suburb of Alpine, died Saturday of complications of stomach cancer, his daughter, Pattie Watson Price, told The Associated Press on Tuesday.
Born in 1912, Watson made his film debut as a baby. He was one of nine siblings who all went into the movie business, as did his father, Coy Sr. The family was honored with a star on the Hollywood Walk of Fame in 1999.
"Acting to our family was not a business. It was our life. We never knew anything but the movies," Watson told the San Diego Union-Tribune in 2002.
His father was a cowboy who lived on the edge of downtown Los Angeles when that area was still rural, and he rented horses to the makers of some of Hollywood's earliest Westerns.
That led the elder Watson to a long career behind the camera in special effects and as an assistant director.
Coy Jr. recounted in his memoir, "The Keystone Kid," how Sennett once blew up his family's porch for a scene in a "Keystone Kops" film then rebuilt it for them, adding a new kitchen and bedroom.
In addition to Keystone Kops movies, young Coy appeared in films of such stars as Roscoe "Fatty" Arbuckle, Mary Pickford, Jackie Coogan and Douglas Fairbanks Jr. In 1925, he played the heroine's little brother in the original film version of "Stella Dallas."
His last film was 1930's "Puttin' on the Ritz," but his daughter said he never adapted to talkies.
"He said none of the people involved in motion pictures liked the transition," Price recalled. "When they made silent movies everybody could laugh and joke and have a fun time on the set. When talkies came along, everybody had to be quiet."
Watson moved behind the camera, working at Acme News Pictures, which had been founded by his uncle, George Watson, the first full-time news photographer at the Los Angeles Times. Among young Watson's assignments was covering the 1932 Los Angeles Olympics.
He also took pictures for local newspapers and was later active in television news, filming for Los Angeles stations and for the early celebrity news program "Hollywood Reel."