Ahmed al-Ansari, the head of ambulance services, said four people were killed and 17 others were wounded in the late Sunday attack, updating an earlier toll.
Officials said an eight-year-old girl was among those killed.
Late Sunday, a gunman riding on the back of a motorbike sprayed bullets at a group as it emerged from a wedding service at the Church of the Virgin in the working class neighbourhood of Al-Warrak.
The assault is the first targeting Christians in Cairo since the military ousted Islamist president Mohamed Morsi on July 3.
Police on Monday were searching for the attackers.