<P> While the three sons were always central to the storyline , several major changes took place by the late 1960s . In the spring of 1967 , the ratings for the series began to sag and My Three Sons finished its seventh season in 31st place in the Nielsen ratings . It was decided that the 1967 - 1968 season would bring the program not only a new time slot , but also new storylines to spice up the ratings . In the fall of 1967 , CBS moved My Three Sons to Saturday night at 8 : 30 pm . In the season - premiere episode , `` Moving Day '' , the Douglas family and Uncle Charley relocate from the fictional town of Bryant Park in the Midwest to Los Angeles . Robbie ( Don Grady ) marries his classmate / girlfriend , Katie Miller ( Tina Cole ) . Tina Cole , in fact , had appeared in different roles on three previous episodes of My Three Sons : `` House For Sale '' from the fourth season ( February 13 , 1964 ) , `` The Coffee House Set '' from the fifth season ( November 19 , 1964 ) , and `` Robbie and the Little Stranger '' from the sixth season ( February 17 , 1966 ) . At the end of the 1967 - 1968 season , the ratings had improved from the previous year with the series placing at 24th in the Nielsens . The following season , the newlyweds discover that Katie is pregnant , and she gives birth to triplets named Robert , Steven , and Charles . Although originally played by sets of uncredited twins , these babies were played uncredited by Guy , Gunnar , and Garth Swanson . The most familiar triplets in the show 's last two seasons are played by Michael , Daniel , and Joseph Todd . </P>
<P> While the three sons were always central to the storyline , several major changes took place by the late 1960s . In the spring of 1967 , the ratings for the series began to sag and My Three Sons finished its seventh season in 31st place in the Nielsen ratings . It was decided that the 1967 - 1968 season would bring the program not only a new time slot , but also new storylines to spice up the ratings . In the fall of 1967 , CBS moved My Three Sons to Saturday night at 8 : 30 pm . In the season - premiere episode , `` Moving Day '' , the Douglas family and Uncle Charley relocate from the fictional town of Bryant Park in the Midwest to Los Angeles . Robbie ( Don Grady ) marries his classmate / girlfriend , Katie Miller ( Tina Cole ) . Tina Cole , in fact , had appeared in different roles on three previous episodes of My Three Sons : `` House For Sale '' from the fourth season ( February 13 , 1964 ) , `` The Coffee House Set '' from the fifth season ( November 19 , 1964 ) , and `` Robbie and the Little Stranger '' from the sixth season ( February 17 , 1966 ) . At the end of the 1967 - 1968 season , the ratings had improved from the previous year with the series placing at 24th in the Nielsens . The following season , the newlyweds discover that Katie is pregnant , and she gives birth to triplets named Robert , Steven , and Charles . Although originally played by sets of uncredited twins , these babies were played uncredited by Guy , Gunnar , and Garth Swanson . The most familiar triplets in the show 's last two seasons are played by Michael , Daniel , and Joseph Todd . </P>
who played the triplets on my 3 sons
who played the triplets on my 3 sons
Guy , Gunnar , and Garth Swanson Michael , Daniel , and Joseph Todd
Guy , Gunnar , and Garth Swanson Michael , Daniel , and Joseph Todd