What were the original first names of the sons on 'My Three Sons'?

Mike, Robbie and Chip (Richard) were the original sons from 1960.
Ernie joined as an adopted son in 1963.
Mike left in 1965.
In 1970, Steven remarried, acquiring a stepdaughter Dodie (Dorothy).

http://www.imdb.com/title/tt0053525/

That's easy! Mike, Robbie and Chip. Ernie came in as a replacement son after Mike got married and moved away.


Here's the link, but I swear I knew this before I looked at IMDb.

http://www.imdb.com/title/tt0053525/

mctavish99, According to this, from the trivia section of the My Three Sons IMDb page, there was not a two year overlap involved in the Mike to Ernie transition. That is the way I remember it happening too.

"Although officially leaving after the show's fifth season in 1964-1965, Tim Considine's last appearance as Mike, the eldest son, was actually in the first episode of season 6 (the series' first in color). The episode opened with a brief scene showing Mike and Sally's (Meredith MacRae) wedding. The episode also "launched" Barry Livingston ("Ernie") as the new son. The characters of Mike and Sally were mentioned in the next two episodes, which dealt with Ernie's adoption, and in a subsequent episode when Charley and the boys thought Steve was getting married. Mike was referred to by name one last time in the first 1966-1967 episode, when the gang visited Steve's hometown. After this they were never referred to by name again for the remainder of the series, although Mike was indirectly referred to as, "the first of you" by Steve a few years later."

The "Mike Douglas Kiss-Off" is a reference to a character whose departure is explained – such as a marriage, or college – but whose name is never again referenced. For the last seven years of the series, Mike Douglas seemingly vanishes from existence, even while relatives marry, graduate, have children, et cetera.

https://en.wikipedia.org/wiki/My_Three_Sons

To clarify my earlier comment, which was intended to condense much information into few words:-

The character Ernie was introduced in October 1963 (Season 4, Episode 7), but he did not appear yet in every episode. His adoption into the family came, as tim10001 says, shortly after Mike's departure at the beginning of Season 6 (September 1965).

http://www.imdb.com/title/tt0053525/
(Information extracted from the episode guides)