Then, on November 3, 2000, a stroke erased the first 13 months of her life.
Her parents were out of town. They'd traveled from Olathe to Honolulu to celebrate their fifth wedding anniversary. Olivia was staying with Jeff's parents, Doris and Clifford Johnson, at their Raymore home.
When Doris looked in on her before heading to work, Olivia was sleeping soundly. An hour later, Clifford peaked in on his granddaughter.
"She was all rigid, and her little arm would jerk every now and then," he recalls.
Soon, Olivia was surrounded by doctors in the Children's Mercy Hospital emergency room.
Her eyes were open, Clifford says, but she wasn't present. When he quacked like a duck a game they often played she didn't respond.
Over the next few hours, hospital workers shuttled Olivia from brain scans to blood tests to two spinal taps. When Michelle walked into the intensive care unit after a rushed return across five time zones, Olivia was in the middle of a seizure.
For 48 hours, physicians didn't know what was wrong with her. Then they gathered the family in a conference room and, pointing to a darker section on the scans of Olivia's brain, told them it had been a stroke.
Jeff went home and began scouring the Internet for information about her prognosis. "But I quit looking," he says. "It freaked me out. It looked like a pretty bleak picture, as far as her future."
With extensive therapy, doctors said, Olivia would regain the use of her now-weakened left side. If she was lucky, when she started kindergarten in four years, the other kids might never know the difference.
"I just assumed, she's going to end up being normal," Doris says.
Now 7, Olivia wears bright-pink glasses, and her blond hair is pulled up in a high ponytail that bobs back and forth as she races around the living room. Sporting a red Nike tracksuit, she tells her grandma to watch as she jumps. Bored with the Legos scattered across the floor, she pounces unexpectedly on her grandfather as he sits on the couch.
"Hey, monkey," he says.
"I'm not a monkey. I'm a puma," she replies with a grin.
She's also one of a tiny number of children who have had a surgery that's inconceivable to most people outside the field of neuroscience. The stroke permanently disrupted delicate connections in Olivia's brain. As she grew older, that damage led to daily seizures that robbed Olivia of her playful independence and her ability to learn kindergarten concepts. Eventually, Jeff and Michelle Johnson realized the only alternative for their daughter was the most terrifying one.
Three out of every 100,000 children suffer a stroke before they're 18. Approximately 10 percent of those strokes are fatal. Even if a child survives it, a stroke is a brain killer.
"If you look at a brain scan months later, you'll see a hole where that tissue was lost and will never come back again," says Dr. Bradley Schlaggar, a pediatric neurologist and professor at Washington University in St. Louis.
After 17 days in the hospital, Olivia started what would be years of physical therapy.
Her memories from life before her stroke told her that she knew how to walk; her therapists insisted that she learn how to crawl first. At times the Johnsons had to confine the energetic toddler to a laundry basket to keep her from using the couch to pull herself up before she was ready.