The attack struck an apartment building overnight. Among the four family members killed were the father, mother and two children.
Another 12 people were injured, according to the civil defense in the Hamas-controlled Gaza Strip. Israel has not yet commented on the incident.
Since Israel and Hamas signed a ceasefire in October, more than 1,000 Palestinians have been killed in the Gaza Strip, according to local authorities.
Israel claims that it is continuing to fight the extremist group Hamas and has expanded the area under military control.
