The identity of Jaycee Lee Dugard, now 29, was revealed when she accompanied Phillip Garrido for questioning by his California parole officer. Garrido, a convicted kidnapper and rapist, also was accompanied by his wife Nancy and two young children that Garrido said were his.

Undersheriff Fred Kollar said in a news conference that Jaycee was the mother of the two young children who had been fathered by Garrido.

Jaycee, who Garrido had renamed Allissa, was reunited with her mother Terry Probyn today, and the mother told ABC News that her daughter had been held against her will all these years and confined in a box in the back of the Garrido's house.

Kollar said that Jaycee had been held captive at a house in Antioch, Calif., since the day she was abducted and none of their neighbors ever knew.

He described the location as a "hidden back yard" within a larger yard that was arranged in such a way "to isolate the victims from outside contact."

Entrance to the secret yard was guarded by a 6-foot-tall fence, tall trees and a tarp, he said.

Kollar said Jaycee and the two children lived a series of sheds, including one that was soundproofed and that could only be opened from the outside. In addition, there were two tents in the yard.

"None of the children had ever gone to school, they had never gone to a doctor," Kollar said. "They were kept in complete isolation."

When asked about Jaycee's condition, the undersheriff said, "She is in good health, but living in a backyard for 18 years does take its toll."

Jaycee was with her mother today along with her two children, ages 11 and 15.

Garrido had been called in for questioning by his parole officer after being alerted by University of California-Berkeley campus security that Garrido was acting suspiciously.

When Garrido showed up for his grilling, there was difficulty in establishing the identity of everyone with him, said Scott Kernan, undersecretary for operations of California's Department of Corrections and Rehabilitation.

Under questioning, Garrido admitted to having kidnapped Dugard when she was 11 years old.

"There is nothing to indicate this was anything other than a stranger abduction," Kollar said. "No connection to the family. They literally snatched her off the streets."

Officers were convinced that Garrido was telling the truth when he and Jaycee told them details that only the kidnapper and victim would know, Kollar said.

Both Phillip Garrido, who is a 58-year-old registered sex offender, and Nancy Garrido, 54, are being held on $1 million bail, charged with kidnapping to commit rape.

The stunning news that Jaycee was alive and had been found elated Jaycee's parents.

"I had personally given up hope," her step-father Carl Probyn said. "I had just hoped for a recovery" and to find the people responsible.

Instead, he said, "I've actually won the lotto."

But as the day wore on and details emerged of Jaycee's ordeal, Probyn became distraught.

Breaking down in tears, Probyn told ABC News, "My girl has no proper schooling and I don't even know what shape she is in. I don't know if she was treated like an animal. ... This is so horrific, I don't believe it."

Jaycee Dugard Snatched on Way to School Bus

 On June 10, 1991, Probyn watched his long nightmare begin to unfold. His daughter was hurrying to catch a school bus when he heard her scream. He looked up to see his Jaycee disappear into a strange car.

"I saw them pull her in and I tried to get her," Probyn said.

The kidnapping terrified the community and led to a massive manhunt.

His wife, Terry, who now lives in Orange County, left for northern California at 6 a.m. today, joining the couple's 19-year-old daughter, who was just a year old when her sister Jaycee was kidnapped.

"She's in shock," Probyn said of his wife. "I told her and my daughter to sit down there and think of questions to ask her."

"She sounds like she's okay," Probyn said. "She had a conversation with my wife and she remembers things. I hope she's been well treated this entire 18 years."

Jaycee's abduction tore at the entire family.

"I've gone through hell," Probyn said, noting that investigators and even members of the extended family looked at him suspiciously for months afterward.

He and his wife, though still legally married, were separated.

Now, Probyn just wants to find out who the people are that took his daughter and why they did it. And of course, he wants to see the now-grown woman he thought was gone for good.

Phillip Garrido was paroled in 1999 after serving prison time for kidnapping and forcible rape. Kernan said that he wore a GPS monitor as part of his parole.

Lt. Les Lovell of the El Dorado County Sheriff's Office, who was a detective assigned to the case back in 1991, said she appeared to be in good health.

Helen Boyer, the Garridos' neighbor for more than 10 years, said she would be completely shocked if it turned out they had something to do with Jaycee's kidnapping.

"There was no girl living next door, as far as I knew," she said.

Boyer said the couple were caregivers to Phillip Garrido's bedridden mother. They would sometimes have three young blonde girls -- friends of the family, she said -- come visit.

"They were real good neighbors," she said. "Real nice people."

Jaycee Dugard's Rescue Gives Hope to Others Whose Children Are Missing

Ernie Allen, president of the National Center for Missing and Exploited Children, told ABCNews.com today that while remarkable, the possible discovery of Jaycee reinforces data that shows kidnappers who are not related to the child typically aren't child killers.

"The Jaycee Dugard case is huge," he said. "There are some people who assume that when a child disappears, there is no hope.

"This provides hope," he said, "for so many searching families."

Many children abducted in the same manner as Jaycee do not have such a happy ending.

Though the country rejoiced when Elizabeth Smart was found alive months after the 14-year-old was snatched, many abducted kids are never heard from again.

One of the most famous missing children cases is that of Etan Patz, the Manhattan boy who disappeared while walking to a school bus in Manhattan in 1979. Despite 30 years of investigations and theories, no trace of the boy has been found.

In June, it appeared that a boy who disappeared in 1955 had turned up alive. John Barnes of Michigan was convinced that he was actually Stephen Damman, snatched from his stroller when he was 2 years old and living on Long Island, N.Y.

Stephen Damman's 78-year-old father, Jerry Damman, became hopeful that he was finally being reunited with his son, but DNA tests dashed his dream.

"It's disappointing and it's too bad we had to go through all of this for actually nothing in the end," Damman said after the results of the tests were revealed.

Steven Stayner also was a prominent case of a kidnapped boy. He was a California boy who was snatched at the age of 7 in 1972. Nine years later, he went into a police station after his captor had grabbed another boy.

"I know my first name is Steven," he told police.

Stayner's story later became a television movie.

More recently, in 2007, Shawn Hornbeck, and a second missing boy were found in a Kirkwood, Mo., after Hornbeck allegedly had been held prisoner for four years after vanishing from a St. Louis suburb at age 11.

SARAH NETTER and SABINA GHEBREMEDHIN

Source: abcnews.go.com