Liberal MPs have attacked the "rioting" students who took a day off school to protest the government's climate change policies, with one challenging them to swear off ice-cream to lower emissions.

An estimated 15,000 students marched in cities and regional towns around the country on Friday - despite warnings they could face disciplinary action for not attending school.

Students hold placards during Friday's climate protest in Melbourne. Credit:Luis Ascui

Liberal senator James McGrath identified a spelling error in a placard held by one student at the protest, circling it in a photograph he posted on his Facebook page. The sign, which targeted Prime Minister Scott Morrison directly, misspelt "jealous" as "jelous".

"Given some of the creative spelling on display at yesterday’s [Queensland Teachers Union]-endorsed muck-up day, perhaps these children’s teachers and parents might like to refocus their attention on the three Rs, of which rioting is not one of them," Senator McGrath said.