CHICAGO -- Max Gomez was a bright-eyed 5-year-old happy to have just started kindergarten when he developed sniffles and a fever. His mother figured it was only a cold.

Three days later, the Antioch, Tenn., boy was dead, apparently from the H1N1 flu virus, commonly known as swine flu.

At least 76 American children have died from the new virus, and doctors are urging parents to watch for warning signs that the flu has become life-threatening.

Ruth Gomez said Max developed dangerous symptoms -- bluish fingers and extreme fatigue after seeming to get better -- just one day before he died. She took him to the doctor, but it was too late.

"We were in shock," Gomez said softly, still trying to wrap her mind around her little boy's Aug. 31 death. "There are so many unanswered questions. What happened?"

It's a question on other parents' minds, too: How can they protect their children from swine flu until the vaccine is widely available?

Swine flu has probably infected hundreds of thousands of youngsters nationwide, but deaths among children are rare.

Health officials are keeping track of children's flu deaths, but they say it's impossible to count all flu cases. So they don't know what percentage of children's infections are fatal.

Many experts say the H1N1 virus does not appear to be more dangerous than other flu strains, but children have been catching it more easily than seasonal flu.

Last week alone, officials reported 19 new cases of children who died, according to the federal Centers for Disease Control and Prevention. And the 76 swine flu fatalities since April compare with 68 pediatric deaths from seasonal flu since September 2008.

Because children seem so vulnerable to it, "every medical epidemiologist in the country" is tracking how it affects them, said Dr. Susan Gerber, an associate medical officer for the public health department in Cook County, Ill.

Most children will recover, but "it's still very concerning and needs to be watched very closely" Gerber said.

Dr. Kenneth Alexander, the University of Chicago's pediatric infectious disease chief, said both kinds of flu have common signs to indicate when they turn dangerous.

Flu viruses can damage cilia, the hairlike fibers lining the respiratory tract that move bacteria and mucous "where we can cough them out" of the lungs, he explained.

That can make people susceptible to pneumonia and other bacterial infections -- a scenario blamed for many flu deaths in otherwise healthy children and adults, he said. In these cases, flu patients often appear to get better, but then fever and a cough return.

Authorities urge parents to seek immediate help if emergency warning signs develop.

Parents should also seek medical help if flu symptoms develop in children most vulnerable to flu complications: those younger than 5 or with high-risk conditions, including asthma and other lung problems; cerebral palsy, epilepsy and other neurological diseases; heart, kidney or liver problems; and diabetes.

A recent report from the CDC found that one-third of pediatric deaths from the new H1N1 virus were in children such as Max, with no known underlying condition that would put them at risk.

Authorities are walking a fine line between making sure parents are vigilant without raising undue alarm.

Commenting on the recent deaths in his state, New Mexico's health chief, Dr. Alfredo Vigil, told residents not to panic, but to take swine flu seriously.

That means kids should get vaccinations for both ordinary flu and swine flu when the vaccine is available, and stay home from school if they are sick.

Parents should stress hand-washing and covering coughs.

Mild cases should be treated at home with rest and plenty of fluids, but parents should call their doctor if more serious symptoms develop.

"We definitely don't want to suggest to someone who has a very sick child that that child should be at home. But at the same time, we don't want lots of children with mild illness showing up" in emergency rooms or doctors offices, keeping doctors from treating sicker patients, said Dr. Michael Landen, New Mexico's deputy state epidemiologist.

In rare cases, swine flu symptoms turned from bad to worse so quickly that by the time of medical attention it was too late. That can occur with seasonal flu, too, Landen said.

Ruth Gomez says that's what happened with her son. Test results are still pending, and swine flu has not been ruled the official cause of death, but Gomez, who once worked as a medical assistant, says doctors found nothing else.