My Three Sons Season 9 Episode 15
Although Katie confidently calls the look-alike triplets by name, other members of the family doubt her accuracy, and when Steve helpfully bathes them, she admits that she can no longer tell them apart because he washed off the inkdots put on their feet. They must be taken back to the hospital for proper identification.
Serie: My Three Sons
Episode Title: Three's a Crowd
Air Date: 1969-01-11