(CNN) -- An 8-year-old autistic boy who went missing from a central Virginia park five days ago was discovered alive Friday at a nearby quarry, authorities said.
"Robert is a very strong and determined little boy," Robert Wood Sr. said in a statement released hours after his son was found. "We never gave up hope that he would return home safe."
A citizen involved in a large-scale search spotted Robert Jr. about 2 p.m. Friday in a creek bed just off a roadway at a Martin Marietta quarry, said Hanover County Sheriff's Lt. Col. David Hines.
Found curled in a fetal position, the boy was "in serious but good shape," Hines added. "Whenever a child is missing, everyone steps up. And that's what happened today."
Robert was taken by helicopter to the Children's Hospital of Richmond, where he was reunited with his family about 3 p.m.
Dr. Christopher Woleben told CNN late Friday that the boy -- who cannot speak, due to his autism -- was "awake, alert (and) surprisingly interactive" when he got to the emergency room.
"He was excited to see his mother, smiling every time he saw her," Woleben said. "He did have some signs and symptoms consistent with cold exposure, and we did a pretty thorough medical investigation."
The boy wandered away Sunday while on a hike with his father, father's girlfriend and his younger brother at the 80-acre North Anna Battlefield Park, according to CNN affiliate WTVR. The park is in Doswell, about 45 miles north of Petersburg and 80 miles south of Washington.
In subsequent days, approximately 6,000 volunteers had joined roughly 300 rescuers looking for young Robert in and around the Civil War battlefield. The boy was found between 3/4 of a mile and one mile from where he was last seen, according to Hines.
The lieutenant colonel said authorities had to turn volunteers away because of the strong desire to help, applauding their service.
So, too, did Robert Wood Sr. He thanked those who had helped, and offered thoughts and prayers, and assisted in other ways.
"The support we have received is overwhelming," the father said.
Barbara Locker, the boy's mother, said in a statement Friday that her child was "here and safe" and "a strong little fella."
Woleben, the emergency room physician, called it remarkable that Robert -- given his age, diagnosis, as well as the conditions outside -- appeared so positive and alert after his discovery.
"It is an amazing story that he was able to survive that amount of time on his own," the doctor said.
Read more about this story from CNN affiliate WTVR.