Just short of one year old, Evan Stauff is a beautiful baby boy who gurgles and giggles like many others his age.
"He was born, I thought, much stronger than our other two sons when they started to develop," said Evan's father, Dave Stauff. "We kept saying, 'Wow, he is really developing quickly.'"
But now when Evan should be about to say his first words, his language development is lagging and he has trouble moving his right arm and leg. Even so, Evan is a medical miracle.
The little boy's rapid development stopped abruptly last April 1, April Fool's Day, an irony his family always mentions.
His mother, Kathleen Stauff, explained how terrified she was when she watched her son have his first seizure.
"I woke up to get up that morning and he was laying in the bed, having a seizure," she said. "I asked Dave to turn the lights on."
"At that point, I had never seen a seizure," her husband added. "To me, a seizure was like something you'd see on TV."
Evan's parents used a cell phone to capture video of their son that morning while he was seizing. His mother said Evan was non-responsive.
"His whole body was rigid," she said. "His breathing was very shallow and fast. His eyes were fixated."
The Stauffs rushed their son to his doctor, and from there to the hospital. Doctors tried to control Evan's apparent epilepsy with medication, but nothing worked.
Evan continued to have waves of seizures, possibly hundreds of them every day. His parents recorded them on video and counted the number of spasms.
"It continued to progress," said David Stauff. "If anything, they were worse. ... Sometimes he'll almost bend in half. ... Other times, it's very slight."
As a school administrator well-versed in special education, Kathleen Stauff understood that Evan's condition was serious. David, a Coast Guard veteran who used to work on rescue boats, quit his job to take care of his son.
After many doctor and emergency room visits, it became clear that the seizures could not be controlled. The Stauffs eventually traveled from their home in North Bend, Ore. to the Mattel Children's Hospital UCLA in California, where they met with Dr. Gary Mathern, the neurosurgical director of the Pediatric Epilepsy Surgery Program.
After looking at a video clip of Evan's seizures, Mathern described them as "hiccup-like." The infant's body tightened repeatedly, almost as if he was responding to a hiccup.
"They go again, and again, and again," he said while looking at hospital recorded video of the seizures. "The eyes shoot over, and you notice his discomfort. He does it again. The eyes shoot over to his left. Again, it's these crunches."
Evan was diagnosed with infantile spasms, a condition that can stunt brain development, and threaten a child's ability to learn to walk and talk. It can even lead to early death.
"Seizures, in the first couple of years of life, when your brain grows 80 percent of your adult size, are particularly devastating to development," Dr. Mathern said.
According to the Epilepsy Foundation, infantile spasms, also known as West Syndrome, most commonly begin within the first year of life in 90 percent of cases. The causes for the spasms are unknown and they are somewhat rare, affecting only one baby out of every few thousand.
The Stauffs went to see Dr. Mathern because he specializes in a particular operation called a hemispherectomy, in which he removes or disconnects half of the child's brain to stop the seizures. He told the Stauffs that Evan needed the surgery.
"It's a stunning operation," he said. "What you have to understand is that risk to the child for death and severe morbidity from the seizures is actually greater than the operation itself."
"So a child born with epilepsy, by the time they reach 40, 20 percent will be dead from their seizures," he said.
It's a wrenching decision for any parent to agree to have half their child's brain removed and risk death on the operating table, but by the time the Stauffs met with Dr. Mathern, they said they knew it was what they had to do.
"It made sense," David Stauff said. "It may seem very radical, but at the same time, it was so practical for Evan. Remove it. It's not working. It's hurting him. It will kill him. It's worth the chance."
After further tests, Mathern determined the problem was coming from the left side of Evan's brain, the side that controls speech. He prepared the family for possible side effects, such as Evan coming through the surgery with vision problems and loss of motor control on his right side.
At home in Oregon weeks before the surgery, Evan's older brothers, Patrick, 7, and Chandler, 11, seemed very supportive and optimistic of their younger brother's surgery.
"When he grows up a little ... his right eye will just be blanked," Patrick said.
"He won't see anything out of the corner of his right eye," Chandler said. "He'll be a lefty, so he'll write with his left hand."
"And sometimes he'll limp when he gets older and he walks," Patrick added.
"Yeah, he'll be different from us, and we'll still love him," Chandler said, kissing Evan.
In describing his decision to go ahead with surgery, David Stauff said, "I don't care if he can't ever walk a straight line or move his arms above his head. Just to look at each and every one of us and know who we are...That is huge."
Evan's parents brought their young son in to UCLA before dawn on Nov. 23. A surgical team went to work inside of Evan's head in an 11-hour-long surgery. Afterwards, the Stauffs visited their youngest child in his recovery room.
"We haven't had any seizures and he's smiling," Kathleen Stauff said, "just getting back to normal."
The surgery made an immediate difference for Evan, but the question remains, how can a child live with only half a brain?
Dr. Mathern explained that the brain, particularly in young children, has an incredible ability to rewire.
"There are certain functions on your brain that you can shift from one hemisphere to another," he said. "Language, for example, which in 98 percent of people is on the left side, can be moved to the right if you operate early enough."
Mathern said that a hemispherectomy patient's resulting I.Q. often depends the health of the remaining half of the brain and much damage the seizures caused before surgery. But personality, he said, is not affected.
"I have taken out right hemispheres, I have taken out left hemispheres, and the kids come out with the same personality they had before," he said. "So, I don't know where personality is."
At least 217 of these operations have been performed at UCLA, with the loss of only one child in surgery.
Now more than a month after his dramatic surgery, Evan is aware and chattering. His father said the results are "night and day" to how his young son used to function.
"To move his legs like this and his arms, to wave them around and to speak is just remarkable," he said. "It's incredible."
While the long-term effects on Evan's development remain to be seen, for now it appears that Evan has a fresh start on life. It's possible that one day, people will never know that he and other children who undergo the operation only have half a brain.
To learn more about Evan Stauff's incredible surgery and how he's progressing, visit the family's website HERE.
ABC News' Lauren Effron contributed to this report.