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HOUSTON — Mona Saldivar can't bear to talk about the day her four children died, swept away with their great-grandparents by Hurricane Harvey floodwaters.

But, she says, she wants the world to know about 16-year-old Devy, 15-year-old Dominic, 8-year-old Xavier and 6-year-old Daisy.

"They were happy kids and they were loved by many people," she told NBC News on Friday. "The time they had here with me — they were happy."

The four siblings drowned Sunday, along with 84-year-old Manuel and 81-year-old Belia, while their uncle Sammy was trying to drive them to dry ground.

Their van had just crossed over Greens Bayou when it was sucked off the road by rushing water. The uncle escaped through a half-open window as the van sank nose-first into the bayou.

He told other relatives that while he was desperately clinging to a tree limb, he could hear the four children screaming and crying as they tried to get out of the vehicle before it vanished from sight.

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The van was found Wednesday with all six victims still inside.

Related: Mexican Relatives of Family Swept Away in Van Can't Cross Border

Mona Saldivar, a dental assistant, said the void left by their deaths is crushing. She hasn't slept, tossing and turning all night. She needs family around her constantly to make it through the day.

She found an old phone that Daisy had filled up with selfies and videos of herself. When she starts to feel distraught, she watches them to ease her pain.

"I'm heartbroken," she said. "I love them so much."

From left; Devy Saldivar, Dominic Saldivar, Xavier Saldivar and Daisy Saldivar Courtesy Virginia Saldivar

On Friday, she spread photos of the children on a table and talked about how she would remember them, her eyes hidden by dark glasses, her foot tapping the floor nervously.

"They were all bubbly and they were social butterflies and always wanted to talk to everybody," she said.

"My son Dominic would ask like a million questions to everybody. It was always one more question. I was like, 'I'm going to make you a T-shirt that says: One More Question.'"

"Daisy, she's a princess. She always wanted to wear princess dresses. Even her big, fluffy Christmas dresses — she would wear them in the summertime.

"My daughter Devy, she wanted to be a veterinarian, so she would feed all the cats in the neighborhood. I would have like 20 cats outside my house."

She said she has been touched by the outpouring support for her family, who are making funeral arrangements. She hopes, she said, her children are not forgotten as the city of Houston recovers from the deadly storm.

"Keep them in their hearts," she said when asked if she had a message for the public. "And keep them in their prayers."

Gabe Gutierrez reported from Houston, Tracy Connor from New York.