Turkish health officials have confirmed that a third child who died in eastern Turkey last week was a victim of the deadly strain of bird flu.
The new cases are said to have been in contact with infected birds
The H5N1 strain had already been blamed for the death of the 11-year-old's brother and sister.
The health ministry added that two more people had been identified with the virus in Turkey, bringing the total number of human infections to 18.
Many parts of the country have now been affected by the virus.
The UN Food and Agriculture Organisation has warned that bird flu could become endemic in Turkey and pose a serious threat to nearby and neighbouring countries.
Many are already taking precautions - in Greece, for example, vehicles entering the country from Turkey are being disinfected, and hundreds of vets have been sent to border areas.
The UN's co-ordinator for bird flu, Dr David Nabarro, hopes an international donors' summit in Beijing on 17 and 18 January will raise pledges for the $1.5bn (£850m) needed to help countries implement programmes to stop bird flu.
The new cases of bird flu in Turkey were in the south-east of the country. Officials said both had been in contact with infected birds.
The three dead children found to have been infected with the H5N1 strain were from the eastern Van province. Tests on their six-year-old brother, who was released from hospital last week, showed he did not have the virus.
Dr Nabarro has warned that educating people, especially children, about the dangers of exposure to infected birds is essential in helping combat the spread of the virus.
In other developments:
A senior director of the World Health Organization tells a Tokyo conference that a failure to respond quickly to bird flu could have immeasurable global consequences, and that despite the best efforts of many governments, the threat of a pandemic is continuing to grow
The European Commission holds talks with international health organisations, at which EU states have the opportunity to outline measures they are taking in response to bird flu.