North Vancouver School District has booked a non-instructional day on April 20 — a day when tens of thousands of people celebrate a drug that could be legalized in Canada as early as this summer.

The annual "4/20" cannabis festival in Vancouver, which attracted 35,000 people in 2017, has sparked controversy over crowds, garbage, commercialization and selling products to minors.

After the 2016 event, Vancouver Coastal Health's chief medical officer urged organizers to stop selling pot edibles to minors after 100 people ended up in hospital — some as young at 15 — with edible cannabis products suspected.

A NVSD principal emailed a warning to parents about the coincidence of dates.

Brad Baker said it was an oversight that won't happen again.

"We will obviously look forward in the future when we set our calendars to ensure we do not do that again," Baker told CBC.

A huge cloud of smoke rises above the crowd as 4:20 p.m. rolls around on April 20, 2017, in Vancouver. (Rafferty Baker/CBC)

Day off in Coquitlam, Port Moody and Delta

Baker advised parents to be proactive.

"We don't condone the use of cannabis or marijuana," he said.

While the professional development day only affects five North Vancouver schools, other districts — such as School District 43 which encompasses Coquitlam and Port Moody, and the Delta district — have also listed April 20 as a pro-d day on their calendars.

Kathleen Whyte, whose daughter attends high school in North Vancouver, chuckled when she received the warning email.

"OK, I did think it was kind of funny. It was surprising to me. I hadn't made that connection between those two events before and I think they probably did that same thing. They hadn't really thought about it and suddenly thought, 'Oh! That might be a problem."

Whyte agrees school districts should change the date next year, but does not condemn administrators for the innocent mistake.

"I'm not worried for my own child," said Whyte, whose daughter attends Handsworth Secondary, is off on a band trip the same day.

The Canadian Pediatric Society has recommended that there should be a minimum age limit of 18 for those purchasing recreational marijuana. (Ben Nelms/Reuters)

Prime Minister Justin Trudeau has said part of the goal of legalization is to restrict access of marijuana to minors, in the wake of concerns coming from parents, politicians and the Canadian Paediatric Society, which released a study last year warning of potential dangers of weed use for developing brains.