Well, that's just gross

Jack, a very young lad aged 4 years, says to his father, 'Daddy, Daddy, I want to get married.'

His father explains, 'For that Jack, you have to have a boy and a girl.'

So Jack answers, 'I've already found a girl.'

'Who?' splutters his Dad.

'Grandma,' continues Jack happily.

'Now, let me get this straight,' his father says. 'You want to marry my mother? ................. You can't do that.'

'I don't see why not?' Jack responds, 'You married mine!'