According to the CDC, from the beginning of the AIDS epidemic through the end of 2011 a total of 9,945 cases of AIDS have been reported in the US and 6 dependent territories among children under age 13 at the time of diagnosis.

Source

Centers for Disease Control and Prevention. HIV Surveillance Report, 2011, "Rates of diagnoses of HIV infection among adults and adolescents, by area of residence, 2011—United States and 6 dependent areas"; Vol. 23, Table 6b, p. 34. Published February 2013. Accessed May 21, 2013.
http://www.cdc.gov/hiv/pdf/st…