The Health Canada warning comes after two children from northern Alberta died from a toxic insecticide thought to be aluminum phosphide brought back by the family from Pakistan.
Health Minister Rona Ambrose expressed her condolences to the family, who was attending the funeral of son Zia, 2 on Friday. His eight-month-old sister died Sunday.
"It's a really tragic situation and this is a product that in terms of how it's regulated, is not supposed to be used in homes ever," Ambrose said in Calgary.
"It's a very dangerous pesticide and it needs to be used by people who are trained to use it."
Health Canada said aluminum phosphide is highly toxic to people and animals.
The department said it can only be sold to people with special training and is not approved for use on bedbugs.
It is not clear how the family managed to bring the pesticide into Canada.
Health Canada says people can legally import small amounts of chemical pest control products not registered in Canada for their personal use, but the rules are aimed at products such as insect repellent.
Jason Flint of the federal Pest Management Regulatory Agency said this exemption could also include aluminum phosphide, but said the pesticide is covered by other federal regulations because it is considered to be a dangerous good.
"Under that exemption, a small quantity could come in," Flint said from Ottawa.
"You are not regulated by Health Canada under the Pest Control Products Act, you would still have to deal with the import requirements under transportation of dangerous goods."
These requirements would include declaring the pesticide, meeting labelling and shipping document requirements, and following transportation rules, he said.
The girl and her brother died after their parents placed pellets of aluminum phosphide around their apartment in Fort McMurray to try to kill bedbugs.
A third child remained in critical condition at Edmonton's Stollery Children's Hospital Friday. A friend of the family said the boy's condition was improving and he was to be taken off a ventilator.
Two other children were treated in hospital earlier this week in Fort McMurray and were released to their parents.
Ambrose said Health Canada will not be investigating the poisoning case.
"That would be for the local authorities, but there will be no investigation by us," she said.
— With files from Bill Graveland in Calgary