Legend has it that the dragon has nine sons, but none has grown into a dragon, with each having his own appearance. They are (arranged by the seniority among brothers): Bixi, Chiwen, Pulao, Bi'an, Taotie, Baxia, Yazi, Suanni and Jiaotu.
The so-called "nine sons of the dragon" doesn't mean that the dragon has exactly nine sons. In traditional Chinese culture, the number "nine" suggests a large number and is put in a supreme status. Nine is not an exact number, but a noble number. That's why it is used to describe the number of sons the dragon has.
Source:
http://Traditions.cultural-china.com/en/210Traditions1371.html
