Two boys, aged 6 and 8 years, and a 3-year-old girl were hospitalized with fevers and coughs in the Krabin Buri district of Prachinburi province, said Dr. Charal Trinvuthipong, director-general of the Health Ministry´s Department of Communicable Disease Control.
"These children live in areas where chickens died, and when they got a fever we had to put them in the hospital to investigate whether they got bird flu or not," he told The Associated Press.
"They are listed as cases under investigation, not suspected cases."
A 2-year-old girl in Bangkok´s Minburi district was also hospitalized to be monitored for the virus, he said.
Charal added the Livestock Department has culled chickens in the areas where the children fell sick.
The lethal H5N1 strain of avian influenza devastated poultry farms across Asia at the start of the year, killing or forcing authorities to slaughter tens of millions of birds before it re-emerged in July.
The disease has infected humans and killed a total of 28 people in Vietnam and Thailand this year. On Wednesday, an 18-year-old Thai man who used to raise fighting cocks died from the disease.