In a statement today, Edwards wrote, "I am Quinn's father." He was referring to Frances Quinn, Hunter's little girl who is now nearly 2 years old.
"I will do everything in my power to provide her with the love and support she deserves," said Edwards. " To all those I have disappointed and hurt, these words will never be enough, but I am truly sorry.
Edwards' children from his marriage with Elizabeth are Cate, 27, Emma, 11, and Jack, 9. Because of their varying levels of maturity, they are likely to react to news of their new half-sibling differently, according to child psychologists.
"Usually there is a kind of shock and shame, especially in a situation like this, that comes upon the family and children are not immune to experiencing it," said Diane Kirschner, a Manhattan-based psychologist who has not treated the Edwards' children.
Kirschner said that children coping with such news do so in different ways depending on where they are developmentally in their own lives.
Edwards' second-oldest daughter Emma, suggests Kirschner, might have the hardest time dealing with her father's announcement because she is on the edge of adolescence, a time of turmoil for many pre-teens.
"It's a period where it's natural to feel kind of embarrassed about your parents and what's going on with them and when a child's peer group becomes more important for approval," said Kirschner. "With this in the news, chances are she might feel ostracized or different and that could lead to issues of self-esteem."
"Sometimes you see children, especially in the adolescence age group, conflict with the parent who is causing the problem," said Kirschner. "It could be arguments or acting out of doing poorly in school."
As for the Edwards' youngest child, Jack, Kirschner says that he may actually be affected least by his father's public admission of paternity. The acknowledgement came after repeated denials and at a time when his wife is battling cancer.
John Edwards' Children Have Already Dealt With Scandal
"At that age sometimes kids can just brush it off," said Kirschner. "Unless he's very sensitive – and that would depend on the individual child's temperament – this might not get to him."
The Edwards' oldest child, Cate, has likely already formed opinions of her father after his 2008 mea culpa over the affair with Hunter.
"She's moved away from the family and won't have as much shock over this because she probably already knows about some of these things," said Kirschner. "She has probably formed her own belief system."
That the Edwards children have already dealt with their share of scandal in their short lives is not likely to make their current situation any easier, experts say.
"It's easy to imagine that compounded stress will make things much more difficult for a child," said Robert Scuka, the executive director of the National Institute of Relationship Enhancement in Maryland. "There is much more for them to worry about."
In November 2004, their mother, Elizabeth, announced that she had been diagnosed with breast cancer. After going through remission, she said in 2007 that her cancer had returned and was likely incurable.
Hunter, 45, met Edwards, 56, in 2006 at a bar in New York City. A self-described filmmaker, Hunter helped produce four webisodes that chronicled Edwards' course on the campaign trail. The affair between the two was first reported by The National Inquirer in October 2007, an allegation Edwards fiercely denied.
In July 2008, Edwards was reportedly seen visiting Hunter at a California hotel where she was with her newborn child, and a month later Edwards admited to having an affair with Hunter but not to having her baby.
In August 2008, after months of speculation, Edwards told ABC News' Bob Woodruff that he had, in fact, been unfaithful to Elizabeth with Hunter. At the time, he also denied the possibility that Hunters newborn was his own, saying in the interview, "That is absolutely not true."
And Cate, the oldest Edwards child, has also endured the death of her older brother Wade, who was killed when he lost control of the car he was driving near the family's North Carolina home in April 1996.
"This [news of a half-sibling] will be yet another set of issues these kids will have to overcome and deal with," said Reena Sommer, a Texas-based psychologist who specializes in family issues.
John Edwards' Children Will Likely Eventually Meet
"This was a big secret that was kept from them so it's about a breach of trust," she said.
Even so, the Edwards clan will likely still be curious about their half-sibling, who is, after all, a part of the family, said Sommer.
"There will be this sort of catching up and wanting to know once they hear the news," said Sommer. "Sort of like whenever a baby is born and everyone wants to know if it's a boy or a girl, what it looks like and these kids will want to know if she looks like them."
"There will be a ton of questions," she said.