Books of History mention that Hazrat Abul Fazl Al-Abbas (a.s.) had 5 sons;

1. Obaydullah, 
    2.    Al Fazl, 
    3.    3. Al Hasan, 
    4.    4. Al Qasim and 
    5.    5. Muhammad. 
    6.    History also mentioned that he had 2 daughters. Mohammad Ibn Al-Abbas is mentioned as one of the Martyrs in Karbala. 
Obaydullah son of Al-Abbas Ibn Ameerul Momeneen (a.s.) is been mentioned as the son who left children. All  the grandchildren of Al-Abbas (a.s.) were from the sons of Obaydullah. The grand and great grand children of Al-Abbas (a.s.) are many and they include many Scholars and very pious Momeneen and very respected Personalities in the history of Muslims. Of the well-known personalities from the great grandchildren of Al-Abbas is Al-Hamza who is buried in Al-Midhatiyyah near Al-Hilla and the whole area is now is called after him as Al-Hamza.     
Wassalam.