It's Just a Plant is a children's book. About cannabis. Written and illustrated by Ricardo Cortés, whose lovely illustrations were recently seen in the book Go the Fuck to Sleep, it was first published in 2005 and has been recently reissued. It follows Jackie, a girl whose twitching nostrils lead her to her parents' bedroom one night where they are smoking a joint. The following day, her mother takes her on an educational journey – they meet a farmer, a doctor, a police officer – to learn more about marijuana.

"It makes some people feel happy. Other people say it's 'dreamy'." Photograph: Ricardo Cortés

What right-on parents: they cycle, they have cool art and psychedelic carpets, they get their vegetables for their vegetarian dinner direct from a farmer (Bob, who has a nice sideline growing pot plants), they are politically active, if a little too optimistic. "Any government can make a bad law," says Jackie's mother, explaining why marijuana was banned. "Luckily, where we live people can work together to fix unfair laws." Cortés is staunchly pro-legalisation – this summer, he printed and distributed illustrated pamphlets to try to convince people on jury duty to practise "jury nullification" – returning a not guilty verdict regardless of evidence – in all criminal drug cases in protest at the law.

"I call it … herb, reefer." Photograph: Ricardo Cortés

Many politicians and columnists have criticised Cortés's sympathetic look at cannabis, claiming that he was encouraging children down an evil road of drug abuse. But perhaps it will have the opposite effect. Although you may agree with much of Cortés's message, anything so self-consciously liberal is usually more than a little cringey. If there's one thing that might put children off drugs, it's reading about these groovy parents taking them.

• This article was amended on 28 November 2011. The introduction to the original version stated that Cortés was the author of Go the Fuck to Sleep. In fact he was the illustrator of that book