Police divers in Winnipeg are in the Assiniboine River, searching for Lisa Gibson, 32, the mother of two children who died after being found injured in their home Wednesday.

Police said Thursday they believe Gibson is still alive and were urging her to contact them. They moved to the river Friday after exhausting searches of parks and the riverbank in the family's Westwood neighbourhood.

Police released this photo of Lisa Gibson and are urging the public to keep an eye out for her and alert them if she is seen. (Winnipeg Police Service)

The police boat is anchored by the riverbank, off a park near the Gibson home on Coleridge Park Drive.

A police helicopter was used Thursday and is on standby Friday in case a tip came in about the woman being spotted somewhere.

A baby boy and his two-year-old sister were found in the Gibson home Wednesday morning. They were critically injured and rushed to hospital, where they later died.

Although there had been reports the children died in the bathtub, police spokesman Const. Eric Hofley said the cause of death is still being determined.

Lauren Hope said the vigil was held to show Lisa and her family that many people in the city support them and are mourning with them. (CBC)

In the meantime, officers are focusing on finding Gibson.

"What they’ll find, it’s too early to say," said Hofley. "They go where they feel the best possibilities due to current conditions for recovering Miss Gibson, if that is the case. We are hopeful she’s still alive."

Searchers spent much of Friday focusing on a small portion of the riverbank near the home where the children were found. Hofley said there were three reported sightings of someone who looked like Gibson walking in pyjama pants and looking distraught along those banks on Wednesday.

Post-partum depression a factor in investigation

A police source did tell CBC News they are looking at post-partum depression as a factor in the investigation.

Tara Brousseau Snider, executive director of the Mood Disorders Association of Manitoba, said 80 per cent of new mothers experience difficulties in the days and weeks after giving birth.

They are tired, lose their appetite and lose interest in life because of all the changes in their life, she said. In rare cases, psychosis sets in and some women start to feel they going to hurt the baby or themselves.

"When psychosis sets in, that's when the woman starts to feel she is going to harm the baby and/or harm herself, but it is extremely rare for mothers to kill their children," she said.

Child deaths in Canada In the past five years, 40 children in Canada have been killed by their mothers. About 57 per cent of those cases were motivated by despair, anger or frustration. In that same time period, only one mother in Canada has killed her child and later committed suicide. Source: Statistics Canada

Brousseau Snider said often mothers can become extremely frightened while caring for their children.

"You may end up thinking that you're washing your hands too much and that you want to clean and then that transfers into how you care for your baby [and] that the world becomes very frightening," Brousseau Snider said.

Not nearly enough research is done on the illness and there aren't enough resources to help women who go through it, she added.

"If anybody you know — or you're experiencing that — the only way to get help is to be hospitalized, get on the right meds, keep yourself safe," said Brousseau Snider.

Vigil held in Westwood

Similar remarks were made at a vigil Thursday night to mourn the deaths of the children and support the family.

People at the vigil said they are trying to find hope in the wake of the terrible sadness. (CBC)

"I came out tonight because I want to support Lisa; if she happens to know that there's this many women and people in general that are not judging her and we're not pointing fingers and we just really want to know that she's OK," said Liisa Burgess, one of the approximately 30 people who attended the vigil.

Dozens of those who gathered, many of whom were young mothers, lit candles and sang Amazing Grace on the steps of the Winnipeg Mennonite Elementary school, just up the road from the Gibson home.

Mourners also closed their eyes and joined hands to share a moment of silence, broken only by the cries of infants carried by their mothers.

"To vilify her is not the right thing to do. Our hearts really go out to Lisa and her husband, Brian. We can only imagine how he's feeling right now … and all the people who love them — the friends and family. We're all heartbroken for them," said Lauren Hope, one of the vigil organizers.

"We need to see this [post-partum depression] as a real illness and certainly nothing any mother would do willfully. It could be any one of us."

Many, like Margaret Managh, are trying to find comfort in the wake in what Hope called the "terrible sadness."

"We're really praying that Lisa will be able to come home — if that's to our creator then that's what it is. If not, I hope she can come home and find some peace," Managh said.