Karl Stefanovic has accused environmental activist Greta Thunberg of being “managed” and “used by activists” to influence young people’s view on climate change.

Thunberg has made headlines around the world after she delivered an impassioned speech at the United Nations Climate Action Summit on Monday, in which she condemned world leaders for failing to act on climate change.

Speaking on 2GB’s Sydney Live on Wednesday, Stefanovic said Thunberg was “fired up”.

“I really do feel for her in the respect that she’s not being looked after, she’s got a lot of pressure on her, and I mean everyone can say ‘if that was my kid, she wouldn’t be in that situation’,” Stefanovic said.

“But the problem is, whoever is behind her, the parents who are behind her or whoever’s managing her, she is being managed and her stance is being used by activists.”

He added that Thunberg’s speech affected other children. “We’re seeing our kids very distressed about the prospective changes to climate and that only adds to their burden and adds to their stress.”

The former Today show host also criticised former prime minister Kevin Rudd for coming out in support of the 16-year-old.

Rudd told the ABC that Thunberg represented “the anger of that generation and does so effectively”.

The former PM said, “It might insult a whole lot of middle-aged white guys, because it is not the way that we would talk, or we think that it is inappropriate for a young girl to speak that way, but when I speak to young people around the world, whether it is in China, here in the United States or back home in Australia, frankly there is a rising rage that our generation has failed to step up to the plate.”

Stefanovic said he was one of the insulted “middle-aged white guys”, and that Rudd should “give it a rest”.

“There’s anger out there, of course there’s anger, there’s anger at this kind of activism as well,” Stefanovic said. “I can’t believe he would go and say that.”

One Nation’s NSW leader Mark Latham also suggested on the radio show that Thunberg’s appearance at the event was “a factor” to be considered.

“I think any parent listening would think, ‘would you really put that much pressure on a child in the international spotlight?’” Latham said.

On the same day, Thunberg took to Twitter to address her critics. “As you may have noticed, the haters are as active as ever – going after me, my looks, my clothes, my behaviour and my differences,” she wrote.

“They come up with every thinkable lie and conspiracy theory. It seems they will cross every possible line to avert the focus, since they are so desperate not to talk about the climate and ecological crisis.

“I honestly don’t understand why adults would choose to spend their time mocking and threatening teenagers and children for promoting science, when they could do something good instead.

“But don’t waste your time giving them any more attention. The world is waking up. Change is coming whether they like it or not.”