DENVER -- The number of confirmed flu cases in Colorado has grown to more than 6,300 and includes at least five deaths -- all of them children, the state health department reported Wednesday.

A sixth reported child death is being investigated.

There are 6,306 cases in all, an increase of 1,619 from Monday's toll, the Colorado Department of Public Health and Environment said. The overall number is higher than the number of confirmed cases from the last two seasons in Colorado combined (6,239).

The deaths include a 2-year-old and 4-year-old from suburban Thornton who died this week, state health officials said. Last week, the flu killed a 15-year-old, 8-year-old and a 1-year-old.

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State officials said they were still trying to determine whether the death of a 2-year-old was also because of flu.

During last year's mild flu season, two children in the state died of influenza. The number is considered the usual flu toll for Colorado children.

"Obviously the number exceeds (the norm), and the season is not over," said Dr. Ken Gershman, chief of the communicable disease program at the Colorado Department of Public Health and Environment.

Flu researchers say they expect this year's death toll nationwide from flu-related complications to surpass the average of 36,000.

Dr. Ned Calonge, the state's chief medical officer, said the majority of flu deaths are among the elderly, but "when you have a certain number of cases, it will generate deaths even in kids.

"We had child deaths last year, but not this many this close together," he said.

Colorado had 19 confirmed deaths of all ages from the flu and 748 deaths due to flu and pneumonia last year.

Health experts are warning parents to be extra cautious especially if a child is running a high fever that does not respond to over-the-counter medications, has difficulty breathing, or exhibits fast, hard breathing or cannot drink or keep down fluids.

Texas, a state that has also been hard hit by the flu this year, has reported a few flu-related deaths involving children, which they see every year.