At least 24 members of the Abu Jamea family were killed in the July 20 strike on their home. They included 18 children between the ages of six months and nine years, according to death certificates obtained by The Associated Press.
The apparent target was a local Hamas military commander.
The military said Sunday there was "reasonable suspicion" of a deviation from army procedure. The incident is among eight new investigations announced by the army yesterday.
Israeli human rights groups have demanded an independent investigation of the war, saying the army is not equipped to investigate itself.