The seven-year-old had symptoms akin to severe pneumonia and was on a respirator at a hospital in the capital, a health ministry statement said. Three further people are being tested.
The first possible Thai death from the virus was also reported when a farmer suspected of having bird flu died of pneumonia-like symptoms.
Millions of chickens have been slaughtered across east Asia after the disease was found in Japan, South Korea, Laos, Cambodia and Vietnam, where five people have died and at least 17 others are infected.
Experts say transmission is chiefly caused by direct contact with the birds, which Thailand does not export alive to Europe.
The commission said the risk of contagion from eating poultry was "very low" but gave a warning that meat could be unsafe without prolonged heat-treatment at over 70C.
There is no evidence so far that the virus can be transmitted between humans, but health experts are constantly on alert for mutations that could ultimately trigger a deadly pandemic.
The World Health Organisation, calling the near simultaneous bird flu outbreaks across much of Asia "unprecedented", said it was concerned that a new, virulent strain of influenza could sweep around the world.
It said eliminating the H5N1 bird flu virus "should be given high priority as a matter of international public health importance".
EU officials said the main purpose of the ban was to prevent commercial damage to European poultry farmers and producers. Brussels is concerned that the virus could infect EU chicken farms if left-overs from Thai imports are fed - illegally - to EU birds.
The emergency measures are so far confined to Thailand, which is the EU's second biggest supplier of chicken, exporting 160,000 tons each year. The ban is a devastating blow to the Thai poultry industry, one of the five biggest in the world.
In Suphanburi province, home to one of the two farm boys confirmed to have contracted the disease from playing with dead birds, every chicken is being culled.
The agriculture ministry has ordered the slaughter of all chickens in Suphanburi, the worst-affected province, while about six million birds have been slaughtered throughout the country so far.
Workers in protective clothing descended on farms to spray birds with disinfectant and toss them into bags before dumping them alive in 15ft deep pits holding up to 30,000 birds. They were then covered with powdered lime.
Thailand is a leading exporter of chicken products to British supermarkets, particularly Tesco, which has a considerable presence there. Last year Britain imported more than 12,000 tons of frozen birds, and more than 35,000 tons of nuggets and other processed goods, but no live chickens or eggs.
Until yesterday the Thai authorities insisted that sick birds were afflicted with cholera, not flu.
Mrs Sudarat denied there had been a cover-up, though farmers and government experts too afraid to speak out by name have for days blamed the epidemic on bird flu, accusing the leadership of trying to protect exports at grave risks to public health.
Japan, Vietnam, and South Korea are on a watch list but were exempted from yesterday's ban since they do not export poultry directly to Europe.
