The children are said to have been 12 and 8 years old.
Four members of the Ahmad family were found dead after an Israeli strike hit a house in the Beit Lahiya project in the northern Gaza Strip, a representative of Shifa Hospital in Gaza City said.
The attack reportedly took place after midnight. Israeli attacks are also reported from nearby Jabalia.
When asked by the AFP news agency, the Israeli military said it would "look into" the matter.
Israel and Hamas reached a ceasefire last year, but the Israeli military has nevertheless advanced further into the Gaza Strip and continued to attack from above. According to the Gaza Health Ministry, controlled by Hamas, more than 1,300 Gazans have been killed during the ceasefire.
