In the 3rd year of Hijrah the first son was born to Fatima (S.A.), who was named "Hasan (A.S.)." The birth of this child saved the Prophet (P.B.U.H.) from the torture of the enemies and the sorrow of the separation of friends. He (P.B.U.H.) happily and joyfully visited Fatima's (S.A.) house and took Imam Hassan (A.S.) into his lap and recited Azan and Aqamat in his ears. Then he gave some silver, which was equal in weight of the hair of the child, as alms.
One year after the birth of Imam Hassan (A.S.), Imam Hussain (A.S.) was born. Now the Prophet (P.B.U.H.) got the substitutes for his sons Qasim and Tahir who had died in the childhood, so that God had decided that the race of the Prophet (P.B.U.H.), persists and survives through her daughter.
The dawn of these two stars brought a new horizon in existence wherein the Prophet (P.B.U.H.). Ali (A.S.) and Fatima (S.A.) saw themselves.
The Prophet (P.B.U.H.) thanking God and considering those two children as the substitute of his sons, loved them very much that the world was astonished.
One day, when he (P.B.U.H.) visited Fatima's (S.A.) house he (P.B.U.H.) saw that Ali (A.S.) and Fatima (S.A.) were sleeping and Imam Hassan (A.S.) was weeping due to hunger. The Prophet (P.B.U.H.) slowly picked up the pot, milked the goat, and fed the child who then became silent.
Once, he (P.B.U.H.) was passing by the house of Fatima (S.A.) when suddenly he (P.B.U.H.) heard Imam Hussain (A.S.) crying. He came back to her home and said, "Oh Fatima! Don't you know that I get upset by the weeping of this child?"
One year after the birth of Imam Hussain (A.S.), a female baby was born, who was named "Zainub" and even after another year another female baby, who was named "Ome Kulsum."
"Zainub" and "Kulsum" were the names of the daughter's of Prophet (P.B.U.H.) who died before 8th Hijra. In the 8th year of Hijra a son named Ibrahim was born to the Prophet (P.B.U.H.), who died after one year of his birth.
Now, the Prophet (P.B.U.H.) was only left over with Fatima (S.A.) and her children. He (P.B.U.H.) loved his grandchildren to such an extent that he (P.B.U.H.) never tolerated to get separated from them. Whenever he (P.B.U.H.) went out of the house, he (P.B.U.H.) would always carry one of them on his shoulders.
source : http://www.ezsoftech.com