"Each day that pass, it's getting harder for (the) children," said Mann's sister Shadea Mann-Mayo. "We've been taking it day by day."
The family isn't sure whether foul play could be to blame.
Mann and the father of one of her children, 70-year-old Carl Adams, disappeared December 19.
Her relatives are watching over her children, while also praying and searching.
"I'm very grateful and I thank God for my family because we've all been in this together. It's been hard on all of us," Mann-Mayo said.
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Adams is described as black, about 5-7, and weighing about 150 pounds. He was last seen wearing an olive green jacket, blue jeans, and fishing hat.
Mann is described as black, about 5-3, weighing about 100 pounds. She has short, straight black hair, brown eyes, a tattoo on her left arm, and a scar on her forehead.
The Durham Police Department is investigating and said the couple could be in a gray 2015 Toyota 4 Runner.
Anyone with information on their whereabouts is asked to call Cpl. M. Richards at (919) 560-4440, ext. 29320, the Durham Police Department's Main Desk at (919) 560-4427, or 911.