Ali bin Abi Talib (may Allah be pleased with him) narrated that :
the Messenger of Allah said, about urine of a male child that suckles: The urine of the boy is sprinkled, and the girl's urine is washed. Qatadah (one of the narrators) said: This is so, as long as they do not eat, when they eat, then both of them are washed.