Michele Haddon/USA TODAY/Imagn
Heavy rainfall quickly dumped up to 6 inches of water in parts of Bucks County, Pennsylvania.
CNN  — 

Authorities have identified the two children still missing nearly two days after they were swept away by turbulent floodwaters that killed their mother.

Matilda “Mattie” Sheils, 2, and her 9-month-old brother, Conrad Sheils, vanished after intense flooding engulfed parts of southeast Pennsylvania on Saturday evening.

Upper Makefield Township Police Department
Mattie Sheils, 2, and Conrad Sheils, 9 months, disappeared as floodwater claimed the life of their mother.

The body of their mother, 32-year-old Katie Seley, was found late Saturday.

A family member acting as a spokesperson expressed the family’s gratitude to the searchers at a news conference Monday afternoon.

“Their compassion, kindness and bravery have given us strength in this unspeakably difficult time,” said Scott Ellis, brother-in-law of Jim Sheils, Seley’s fiancé.

Seley was among five people who died after storms pummeled Bucks County over the weekend, according to Upper Makefield Fire Company Chief Tim Brewer.

The Bucks County coroner identified the other victims as Enzo Depiero, 78, and Linda Depiero, 74, of Newtown Township; Susan Barnhart, 53, of Titusville, New Jersey; and Yuko Love, 64, of Newtown Township. According to a news release from the coroner, they all died from drowning. Love’s cause of death was listed as drowning with multiple injuries.

The victims didn’t travel into already high water, Brewer noted at the news conference. “They were caught,” he said. “This was a flash flood. … The wall of water came to them.”

Brewer earlier said officials had tripled the number of resources in the search for the missing Sheils children.

Thanks to improving weather, searchers can use more resources, including underwater and air assets as well as drones and search dogs, to look for Mattie and Conrad.

Upper Makefield Township Police Department
Katie Seley, a 32-year-old mother of three, was killed by ferocious floodwater Saturday.

The family was visiting from South Carolina and were driving to a barbecue when they got stuck in flash flooding, Brewer said Sunday.

The mother and a grandmother grabbed Mattie and Conrad. The father grabbed the children’s 4-year-old brother.

The father and the 4-year-old “miraculously” made it to safety, the fire chief said. But the mother, grandmother and younger children were swept away.

The children’s grandmother survived and was treated at a hospital, police said.

“The mass casualty incident, like these, which we have never seen before, (is) unbelievable and devastating to all the families involved,” he said.

Over the past month, parts of interior New England and the Northeast have seen 200% to 300% of their average monthly rainfall, leading to last week’s disastrous flooding in parts of Vermont, New York and western Massachusetts.

Floods are among the deadliest weather hazards in the US, according to the National Weather Service. It only takes 2 feet of rushing water to carry away most vehicles, including pickups and SUVs, according to the weather service.

A flash flood can happen anywhere intense rain falls faster than the soil can absorb, and generally happen within a short time period after rain, making them more life-threatening, according to the National Weather Service.

CNN’s Sara Smart, Steve Almasy, Kristina Sgueglia, Robert Shackelford, Claudia Dominguez, Christina Maxouris, Lauren Mascarenhas, Melissa Alonso and Caitlin Kaiser contributed to this report.