Yasin Abu Khussa, 10, died in a raid on a base of the group's military wing, the Ezzedine al-Qassem Brigades, at Beit Lahiya in the north of the strip, he said -- one of four strikes the Israeli military said it carried out in response to rocket fire into Israel.
His sister Yasmin, 6, was seriously wounded and his brother Ayub, 13, suffered moderate injuries, al-Qudra told AFP.
The strikes came hours after four rockets fired from the Gaza Strip by Palestinian militants hit neighbouring Israel Friday night without apparent casualties, the Israeli army said.
"There have been seven rockets fired at Israel from the Gaza Strip since the beginning of the year."
Since the end of the devastating war between Israel and Gaza militants in summer 2014, approximately 34 projectiles fired from the Hamas-controlled Palestinian coastal strip have hit the Jewish state, according to military data.
Sunni Muslim militants claiming links to the Islamic State jihadist group have said they were behind rocket fire in recent months, but Israel holds Hamas responsible for all such incidents.