I'm not following you here. The actor that played Mike left the show (because they would not let him direct- that is where his passion was) leaving only 2 sons. They adopted Chip's friend Ernie and he then became the third son (thus keeping the name of the show accurate). It wasn't until much later that Robbie married Katie and they also had 3 sons.
I know, but I'm referring to the very last episode of the show in 1972. She said something about Mike being in the last episode and having 3 kids of his own. What I meant by my post was that I think she is just having a fuzzy memory, and the three children she was referring to were in reality Robbie's triplets and not Mike's.