(McClatchy-Tribune Information Services) -- Judy Pickens' tender attention to her two sick children delighted the medical staff at St. Louis Children's Hospital.

While puzzled doctors tried to battle the tots' mysterious illness, Pickens remained faithfully at their bedsides, changing diapers and linens, and even offering to scrub the toilet.

"It was almost refreshing for us to see a parent so involved with their children's care," said Dr. Jamie Sutherell, who treated Pickens' children Mikal and Kheematah in the hospital in October 2004.

But that loving care hid a horrific secret, prosecutors told a jury Tuesday in St. Louis Circuit Court. While a team of doctors and nurses raced to identify the illness, Judy Pickens was poisoning the children with her own blood pressure medication.

Prosecutor Shirley Rogers said evidence will show that Pickens even crushed tablets and injected them by syringe into her son's intravenous tube at the hospital.

Mikal, 3, died a week after he was brought to the emergency room; Kheematah, then 5, eventually recovered.

Pickens, 38, of St. Louis, is on trial on charges of first-degree murder, first-degree assault and armed criminal action.

The maladies began in September 2004, when the children complained to their teachers of pain in their stomachs. Both were lethargic and sleepy, according to testimony.

Pickens took the children to the emergency room several days later, as they suffered vomiting, diarrhea and dehydration. The hospital sent them home after fluids seemed to help. Pickens brought them back two days later, as their conditions worsened. Both were seriously dehydrated and continued to vomit.

A team of doctors and nurses testified Tuesday about exhaustive efforts to identify the baffling illness. They said they ran dozens of tests -- which all came back normal -- while racing to keep the children hydrated.

The hospital staff struggled to keep an IV in Mikal's small veins; a doctor eventually implanted one surgically in his leg.

Kheematah slowly began to recover. But Mikal's condition went up and down.

The nurses had trouble waking him one day.

The next evening, he began breathing very rapidly. Doctors gave him medicine for asthma but could not find a reason for his trouble breathing. By the early morning hours that Oct. 9, he struggled for every breath.

"He had a fearful look is his eye," Sutherell said. "You could tell he was afraid."

Mikal eventually stopped breathing, and doctors could not revive him.

On the day he died, a nurse noticed a white powdery substance in the tube running to Mikal's intravenous line.

Karen Nichols, another nurse who saw it, said: "I had never seen anything like that in the tubing before."

The nurses threw it away, but someone dug it out of the trash, according to testimony. The family later gave the tubing to Mikal's pediatrician, who had the substance tested and then turned the evidence over to police.

Testimony this week may include discussion of Munchausen syndrome by proxy, a medically recognized psychological disorder and form of child abuse in which a parent, usually the mother, intentionally makes a child ill, often to get attention for herself.

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