"They're frightening the living hell out of kids. It's like child abuse and I think they should be held accountable," he told SBS News on Tuesday.
He said "hostile" and "dishonest" activists were "giving kids nightmares because they don't believe there's a future".
Climate strikers have targeted the outspoken MP who represents the electorate of Leichhardt which covers Cairns and far north Queensland.
"One of them was almost in tears, as far as she was concerned the reef was dead in 10 years ... They only spoke in slogans 'save the reef', 'stop Adani' and '100 per cent renewables by 2030'."
He said Australia needed "solutions not slogans" around climate change.
A war on plastics
Mr Entsch has vowed to legislate a national approach to reducing single-use plastics with the ultimate aim of phasing them out entirely.
But he dismissed the idea the Great Barrier Reef was facing any kind of existential threat, instead declaring his mission is to reduce the amount of plastic in Australia's oceans.
"We don't need to 'save the reef'. The reef is functioning well. There are lots of challenges. We need to continue to manage it and meet all those challenges," he said.
He nominated curbing plastics in the oceans as the main challenge he hoped to address as envoy, committing to a national policy on plastics.
Mr Entsch said he was inspired by the actions of school student Molly Steer, who started the Straw No More campaign.
"What we have in the oceans is horrifying," he said, adding that images of sea life ingesting plastics "keeps me up at night".
What we have in the oceans is horrifying
Mr Entsch said he wanted Australia to develop the "world's best technology for recovering these products once they're out in the environment", which could then be used by other nearby countries.
He advocated eventually phasing out single-use plastics locally and looking for environmentally-friendly alternatives.
The MP also downplayed coral bleaching, saying he was "really concerned [but] bleaching has been happening forever".
Bleaching occurs when warmer ambient temperatures cause coral to expel tiny photosynthetic algae, draining them of their colour.
"In some areas that were most severely bleached a few years ago, the recovery has been phenomenal," the Queensland MP said.
But some scientists do not share Mr Entsch's optimism.
Last month, a study published in the journal Nature found the damage caused to the Great Barrier Reef by climate change had compromised the capacity of its corals to recover
Researchers found the number of new corals settling on the Great Barrier Reef declined by 89 per cent since back-to-back heatwaves bleached the World Heritage site.
They discovered a "crash" in coral replacement compared to levels measured in years before a mass bleaching event.
Professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University, said "there's only one way to fix this problem and that’s to tackle the root cause of global heating by reducing net greenhouse gas emissions to zero as quickly as possible".
Co-author Morgan Pratchett said "we used to think that the Great Barrier Reef was too big to fail - until now".
The Great Barrier Reef is also under strain from an almost-invisible problem.
"Microplastics have been found pretty much everywhere on the Great Barrier Reef," Australian Institute of Marine Science's Frederieke Kroon told SBS News on Tuesday.
"When people think about microplastics they generally think about microbeads, the stuff that's in cosmetics. We've actually never found any of those in our samples ... On the Reef, the microplastics we're finding are mostly fragments from larger bits of plastic," Ms Kroon said.
"One way to think about it is if you have a drinking bottle and it gets smashed around by the waves and then you have the tropical sun bearing down on it ... they're all factors that break down that plastic into smaller and smaller and smaller bits."
She said "bags, containers, food wraps can all eventually break down into microplastics".
"We're not sure yet the potential impact on reef organisms ... [But] it's better not to have it in the environment."