Two of the day's deaths came in an air strike that targeted a motorbike in the Gaza City neighbourhood of Tal al-Hawa.
"Two Palestinians were killed in an air strike on the Tal al-Hawa neighbourhood," Hamas health ministry spokesman Ashraf al-Qudra said, without adding details.
A six-year-old child was killed in another strike in northern Gaza on Sunday evening.
"Hussein Jalal Nasser, six years old, was martyred in an air strike that targeted his house," emergency services spokesman Adham Abu Selmiya told AFP.
The deaths brought to 29 the number of Palestinians killed on Sunday, in the bloodiest day so far of Israel's campaign against the Gaza Strip.
The overall death toll in some 100 hours of relentless Israeli air strikes stood at 75, with at least 700 injured, health officials said.
At least 10 children, five of them babies and toddlers, and six women were among those killed on Sunday, in attacks that came even as diplomatic efforts intensified to broker an end to the bloodshed which began on Wednesday.
The violence has also cost the lives of three Israelis and injured more than 50, according to medical sources.
By far the deadliest strike was in northern Gaza City where a missile levelled a three-storey building, killing nine members of the Al-Dallu family -- five of them children -- and two other people, medics said.
Qudra named the dead as policeman Mohammed al-Dallu, 35, Suheila al-Dallu, 50, Samah al-Dallu, 22, and five children: Jamal and Sara, whose ages were not immediately available, five-year-old Yussef, two-year-old Ranin, and 11-month-old Ibrahim.
The body of another woman from the same family was also pulled from the rubble but her identity was not immediately clear.
The other two victims, who lived next door, were named as Amina Mattar al-Muzzana, 83, and Abdullah Mohammed al-Muzzana, 22, Qudra said.
The Israeli army had no immediate comment on the strike, only saying the air force had hit "a few targets in northern Gaza City".
Shortly afterwards, six more Palestinians were killed in four separate strikes -- two in Gaza City, one on the Jabaliya refugee camp and one on the Nuseirat refugee camp in central Gaza.
In Gaza City, Sami al-Ghafir was killed in a raid on the eastern Shejaiya neighbourhood, and Mohammed al-Awf was killed in the north of the city.
The strike on Jabaliya killed Suheil Hamada and his son Moamin as they were driving a water delivery truck through the camp.
And an early-evening strike on Nuseirat killed two men, Aatiya Mubarak and Hossam Abu Shawish, the emergency services said.
Earlier strikes across the strip killed six more Palestinians, four of them children.
At around 2:00 am (0000 GMT) strikes on the northern town of Beit Hanun killed two toddlers, three-year-old Tamer Abu Saeyfan and his one-year-old sister Jumana.
Several hours later, 18-month-old Iyyad Abu Khusa was killed in a strike east of Bureij refugee camp in central Gaza. His two brothers, aged four and five, were critically wounded in the raid, Qudra said.
Medics later reported finding under the rubble of a house in eastern Gaza City the body of a woman who had been killed in a strike earlier in the morning. They named her as Nawal Abdelaal, 52.
And in the late morning an air strike on a small house in the beachfront Shati refugee camp in Gaza City killed 13-year-old Tasneem al-Nahal and Ahmad al-Nahal, 25, both from the same family.