If he's been in jail for twenty years, how does he have "children?" Yes, he COULD have had them 20 years ago, but then, aren't they a little old to be living with him? This makes no sense, except maybe that conjugal visits were allowed.
There is a bizarre sub-culture of generally unattractive, empty-headed, and/or politically liberal women who take up correspondence with prisoners and end up marrying them. Prisoners are generally allowed conjugal visits and it doesn't hurt their chances in front of the parole board either.
I suspect that's the case here. It's a sick world.