Vanessa Baier's 4-year-old daughter Alexia was in full-on crisis.
"I just kept thinking, 'What's going on with my child?'" Vanessa Baier told "20/20" while fighting back tears.
Alexia had been breaking out into erratic, explosive behavior that would appear completely out of left field.
"It was just swings that were very dramatic and uncalled for, for the situation," her father, Brian Baier, told "20/20."
"There have been times where [her tantrum] was an hour and a half, two hours," Vanessa Baier said.
Alexia, now 8, wasn't always so volatile. Her mother, a special-needs teacher; her father, an accountant; and their oldest daughter, Kyla, had all welcomed a very typical baby girl to their loving home outside Chicago.
"She had such a fun personality. She was always laughing, smiling," Vanessa Baier said.
And as Alexia began attending preschool, her mom said her daughter was excited and loved her new friends and teachers.
"She was on track. She was even advanced in different areas. She was just a typical 4-year-old," AJ McCree, the school's principal, told "20/20."
But in the winter of 2014, Alexia got sick. A doctor diagnosed her with strep throat.
"That was the first time she ever had strep throat," Vanessa Baier said. "No big deal, just run-of-the-mill strep throat."
Alexia was prescribed a typical course of antibiotics, but as the infection disappeared, her bubbly personality began to change.
"It was less than two days later. It was defiance and OCD [behavior]. She just all of a sudden seemed angry," her mother said.
"It really came to my attention that something was off when Lexi would start to destroy the classroom," McCree said, referring to Alexia. "It was a lot of screaming, a lot of hitting and kicking adults."…
"We're trying to team together to try to figure out what's going on, but at the same time it's like this just isn't making sense," Vanessa Baier said. "I don't know how to de-escalate my own child."
This was especially troubling to Vanessa Baier because de-escalating children in crisis is part of her responsibility as a special-needs teacher.
But things became dire when Alexia's prolonged tantrums turned into threats toward her family and herself.
"Telling my 6-year-old (Kyla), 'You have to stay in your bedroom because I don't know what your sister is capable of,' is heartbreaking. She knew the whole time. She had told me, 'Something's wrong with Alexia's brain.' She knew," Vanessa Baier said. "'Something happened because this is not my sister.'"
Vanessa Baier said Alexia knew something was wrong too.
"She would cry and say, 'Mommy, why can't I be good? I just want to be good.' That broke my heart," she said…
Alexia had unbuckled her car seat and started rummaging through her mother's purse. Vanessa Baier pulled over and turned to her daughter.
"As I picked my head up, she was stabbing me in the eye with my mascara wand. I was scared. I was scared for all of our safety," Vanessa Baier said. "This isn't normal, you know. Four-year-olds don't unbuckle their seat belts in the car to stab their mommy in the eye with a mascara wand all over a milkshake."
She called her husband, who was at work.
"He immediately dropped what he was doing and left work. I said, 'You need to stay on the phone this entire time, just in case. If something happens, you need to call 911,'" Vanessa Baier said. "I didn't feel that I was safe, that Kyla was safe or that Alexia was even safe from herself."
Out of options, the desperate parents did what had been previously unthinkable to them: They had Alexia admitted to a psychiatric hospital.
"[It was] the hardest nine days of my life," Vanessa Baier said through tears. "We could only see her for an hour a day. She was allowed to call us once a day. ... For a 4-year-old, those phone calls that she got once a day, she spent crying to me, 'Why did you leave me? I need you. I need you to come back.'"…
About 400 miles away from the Baiers, another family's child was suffering in suburban Minnesota.
Natalie and Brian Barnes' son Parker had been having seizures and dealing with debilitating anxiety, rage and depression for months.
"I would liken it to an abduction. Something came in the window and stole our child and left behind this shell. Our kid is gone!" Brian Barnes told "20/20."
The Barnes family's lives changed in April 2017 when Parker, the oldest of four children, was just 10. He was a rambunctious and outgoing boy. But midway through fourth grade, Parker began acting differently, with odd tics and strange moodiness.
Then one day, his brother Stetson was heading to the family's upstairs bathroom and ran into Parker.
"I'm like, 'Mom! Dad! He's going to stab himself!'" Stetson told "20/20."
"I ran up to the bathroom and there he stood with a knife in his hand," Natalie Barnes told "20/20."
"Bawling uncontrollably," Brian Barnes said.
"He was, like, in a trance, and I just grabbed the knife…
An emergency room doctor recommended that Parker be evaluated by a psychiatrist, and just like the Baier family, the Barneses checked Parker into a psychiatric hospital.
"That was a nightmare," Parker, now 12, told "20/20." "That was like a prison for children 'cause all the children didn't want to see their families, because they were all so like angry or mean or something."
As Parker was evaluated, one doctor became struck by one factor in his case. She learned that Parker's symptoms had first begun months earlier, when he had been diagnosed with strep throat.
"She said he might have something called PANDAS, and we're like, 'PANDAS?'" Natalie Barnes said…
Brian and Natalie Barnes took Parker to more than a dozen doctors in Minnesota looking for a remedy for PANDAS, showing them videos of his erratic behavior. They got limited results.
"I would have to say most the time they would go, 'Hmm.' Nobody ever said, 'O.M.G., I can't believe he's doing that. Let's figure it out!'" Brian Barnes said.
Their quest for better treatment took them to Dr. Beth Latimer, a pediatric neurologist in Washington D.C. who takes on the PANDAS cases that many other doctors don't.
"I have felt tremendous amount of responsibility for these kids," Latimer told "20/20." "I've seen people move from one side of the country to the other. Parents get divorced because they can't deal with the trauma of this illness."…
As a young girl, Kathryn Ulicki, now 12, suddenly started exhibiting bizarre behavior.
Rather than breaking out into screaming fits or convulsions, Kathryn suddenly feared that she would suffer an allergic reaction or be poisoned from food. So one day, she just stopped eating.
"I had no idea what was going on," Michael Ulicki, her father, told "20/20."
Kathryn had a longstanding allergy to sesame, but this level of paranoia when it came to eating was new. Kathryn said she wanted to eat and drink but feared that she would have an allergic reaction.
"I was, like, scared to swallow my own saliva, so I would just spit the whole entire day," Kathryn told "20/20."
It's not clear whether Kathryn had an undetected strep infection or whether the onset of symptoms was triggered by a different infection, according to her parents. But within two weeks of an onset of symptoms, Kathryn, then 9, went into the hospital for dehydration. She stayed there for three weeks. She had a feeding tube for nearly two months. Things only got worse…
But the parents of children believed to have PANDAS say their question is: what do they do if their child does not get better and how long are they supposed to wait?
As Kathryn progressed, the Barnes family continued searching for answers. Natalie and Brian Barnes had every intention of putting Parker through the intensive treatment that Latimer had suggested -- plasmapheresis, a process to remove the antibodies attacking his immune system -- even though it would mean Parker would have to spend a week at a hospital in the intensive care unit…
He and Natalie Barnes began yet another search for another doctor. They were finally able to get an appointment for later this month with a specialist who, they say, is open to the idea of giving Parker plasmapheresis in Minnesota. They estimated that the cost would be as much as $100,000 for treatment and follow-ups.
It was just a few years ago that Alexia was put into a psychiatric ward and prescribed medication for bipolar disorder and schizophrenia. Now at 8 years old, she is thriving. She was chosen out of her entire school as the "Student of the Month" for positive behavior.
Her family said Alexia had responded well to a different antibiotic than the one she'd been given when she first had strep, along with a few other medications. Her parents also are trying everything they can to keep her compromised immune system away from bacteria and infection…
Vanessa Baier said Alexia still has "flare-ups" and they expect to still have struggles with Alexia's health going forward. She has had 15 doses of antibiotics in the last three years.