After his comments, co-host Deborah Knight could be heard asking 'What?' while Jeffreys and entertainment reporter Richard Wilkins concurred: 'That's disrespectful.'
'They are very, very reserved, not like your average Aussie child,' Deborah added.
'I don't want to be disrespectful, but they could be aliens!' he kept going.
When Sylvia and Richard told him that he probably was being disrespectful, Karl asked: 'Well what kids behave like that?'
Deborah said in reply: 'Well people with amazing bringing with multiple nannies perhaps?'
Karl continued, impersonating Prince William in an exaggeratin English accent, exclaiming: 'Do you know what you get when you go inside here? Range Rovers!', implying the royal bribes his children to behave well.
Later, when the Today show crossed to British correspondent Camilla Tominey, who had been waiting outside the hospital, Karl made more odd jokes.
After seeing Prince William and Kate posing outside, just seven hours after giving birth to the newborn, Karl joked that he couldn't believe she would have been able to have looked so refreshed.
'I mean, are we to believe - we are looking at those photos - are we to believe this or could this have happened days or weeks earlier?' he prodded the correspondent.
'I mean, it [Kate] is astounding to me!'
Deborah politely informed Karl that 'it gets easier after your third child.'
'I want to ask another question,' he asked, 'What about when the young ones are going into the hospital?'
'Charlotte and George. Are these children, Camilla, actually real? I don't think I've seen kids this well behaved!'
Camilla admitted that the press and well-wishers who had gathered to watch the kids walk in to meet their brother were 'delighted' and 'amazed' by their behaviour.
'Everyone is looking going, "These are amazing children," it was unreal,' she said.