A spokesman for Egypt's Interior Ministry said two girls less than the age of 10, a 13-year-old girl and a man also were killed Sunday at the Church of the Virgin Mary in al-Warraq, Ahram Online reported.
A witness said a man randomly fired 15 bullets at the wedding before fleeing.
Eighteen people were injured.
Political and religious figures have condemned the attack on the church.
Interim Egyptian Prime Minister Hazem El-Beblawi denounced the attack, calling it a "cowardly criminal act" in a statement.
Grassroots Christian rights group Maspero Youth Union said it held the government responsible for the attack, Ahram Online said.
In a statement, the group condemned the government's failure to protect Christians during the attacks following the Aug. 14 police dispersal of two large protest camps that supported ousted President Mohamed Morsi.
The Maspero Youth Union called for a protest next week in front of Cabinet headquarters to demand the interior minister be tried for his late response to ongoing attacks against Christians.
Various political parties and religious organizations also condemned the attack.
Ahram Online said numerous attacks against churches were reported following Morsi's removal July 3, but most of the attacks were triggered by the Aug. 14 break-ups of the two main pro-Morsi protest camps in Cairo and Giza in which hundreds died and thousands were wounded.
More than 30 churches, 122 shops and 51 houses belonging to Coptic Christians were destroyed in sectarian attacks, mainly in Upper Egypt, a report published in September by the Egyptian Center for Public Policy Studies said.