What does it take to save the life of a 4-year-old boy?

Quick thinking parents, for sure, who pack the child in the car at the first sign of trouble. A triage nurse at the front door of the hospital who looks at Alex Muller — his face drooping on the left side — and first says the word "stroke." Then there is the team of specialists who rush to the emergency room, making quick and critical decisions.

And, for weeks afterward, there are the nurses and rehab specialists tasked with getting the child up and walking again — and who still have the bite marks on their arms to prove it.

But it is perhaps the boy's spirit that is the most powerful force of all.

Now, nearly five months after he suffered a rare and potentially fatal stroke, Alex Muller — a 36-pound, towheaded, Thomas-the-train-loving preschooler — still battles to regain his strength. His left side remains stiff, and he hasn't regained movement in his left arm and hand, which, after the stroke, he affectionately named Lefty.

But he is running and jumping again. And, on a recent day, he walked proudly into his parents' kitchen, holding an iPad under his stiff left arm, and declared proudly: "Look what Lefty can do!"

Last week, Advocate Children's Hospital honored the tiny stroke victim as its "pediatric rehabilitation patient of the year." Doctors had hoped the child might leave the hospital with a walker. His parents had planned to revamp their home for a wheelchair. But instead, the boy walked out the doors of Advocate Children's on June 19 on his own.

"Alex did therapy every day with a smile on his face no matter how hard the activities were," said Colleen Powell, 28, his physical therapist.

Except sometimes he wasn't smiling. When he couldn't do something, the boy would lash out, pinching and biting the people trying to help.

But Powell and other caregivers refused to back off. Instead, they gave him a superhero suit, complete with a blue cape, so while he slowly learned to walk again, he could be Super Alex. With an unsteady gait, he strutted through the hospital hallways, excited to show everyone his suit. He would bounce on a therapy ball and pretend that he was flying. Often, he would stretch out his arms and pretend to soar.

"Alex is a happy boy. He didn't realize how much he went through," said Powell. "He just wanted to play, and (as his condition improved) he was excited to show off the new things he could do. I would come in on Monday morning and he and his dad would have something new to show me, standing by himself or taking some steps."

The last few months have been a tough road for the Muller family. Not too long ago, they — like many people — didn't realize that a child could have a stroke. Experts say that, in general, strokes in children are rare, occurring in about 11 out of 100,000 children ages 1 to 18. More than 100 risk factors have been identified, including heart disease, sickle cell disease and blood disorders. But, in one-tenth of cases of strokes in children, no cause is ever found.

These facts are now well known to the Muller family. But on May 7, when they were flying back from a trip to Disney World, they were blissfully unaware of the path that lay ahead.

On that day, as the plane descended toward Chicago, Alex was sucking on a piece of candy. His parents noticed that he seemed to be drooling from the left side of his mouth. They thought it was strange, but didn't dwell on the moment.

Alex walked off the plane that day and seemed fine. Then, during the car ride home, he threw up. And when he walked into their Palos Heights home, he collapsed inside the doorway. He told his mother that he couldn't get up. The left side of his face drooped. His left arm hung limply at his side.

Lisa Muller swept her child into her arms and put him in the car. She knew something was terribly wrong. She bypassed a local hospital and sped toward Advocate Children's Hospital in Oak Lawn. There, the triage nurse at the front desk looked at Alex and called immediately to the emergency room.

"I need a bed right now," she said, her voice urgent. "I don't know what's wrong, but he looks like he's having a stroke."

Muller could barely believe what she was hearing. A 4-year-old having a stroke?

Within a moment, Alex was on a gurney and surrounded by a team of a half-dozen people. Advocate Children's is a stroke center, and the people who were urgently working on the child were part of the hospital's stroke team.

Their quick response — as well as Lisa Muller's decision to bring Alex straight to the hospital — would be critical in the child's survival and recovery.

Because strokes are not typically associated with children, their symptoms are sometimes missed by parents and even doctors, said Dr. Jose Biller, a neurologist at Loyola University Medical Center, who specializes in strokes and who consulted on Alex's case. The signs of a stroke — such as drooling, slurred speech, clumsiness — are sometimes chalked up to behavior typical of children. And because many other conditions mimic the symptoms of stroke, diagnosis can be challenging, Biller said.

But "time is brain," neurologists like to say. And a quick diagnosis is vitally important to halting the progression of a stroke. Studies show that doctors, in recent years, are getting better at diagnosis, but more awareness is needed, Biller said. "People need to dispel the myth that strokes only occur in older people," he said.

At Advocate Children's, Alex's parents sat vigil. His mother took three weeks off from work, but eventually had to return to her job as a supervisor at a paint company to maintain the family's health insurance. His father, Bob, 39, quit his job as a project manager for a recycling company so he could stay by Alex's side during the day.

The couple have two other children, ages 7 and 11, who also needed care. And so, in the evenings, Bob Muller went home to give them dinner, help with their homework and put them to bed. Meanwhile, Lisa Muller spent every night at the hospital, where she slept — often cuddled with Alex in his hospital bed.

Sometimes Alex would ask: When am I going to be normal again?

Doctors never pinpointed the cause of the stroke that had left him paralyzed on his left side, unable to even lift his head. But as time went on, they felt confident that the danger had passed and the chance of another stroke was extremely low.

Slowly, Alex began to improve.

He relearned how to swallow. Then he gained the strength to sit up. Three weeks after the stroke, he stood by himself for the first time. Two weeks after that, he moved his left arm.

With each improvement, the little boy radiated joy.

"I'm learning to walk again!" he'd call to visitors. "Want to see?!"