The child was killed when a mortar barrage launched from the Gaza Strip hit a car near a kindergarten in Sdot Negev Regional Council near the Israel-Gaza border, Xinhua quoted a spokesperson with the Israeli military as saying.
It is the first Israeli casualty since a fresh round of fighting between Israel and Hamas, the Islamist group that dominates Gaza, started Tuesday, Magen David Adom, Israel's Red Cross, said.
Israel's Prime Minister Benjamin Netanyahu vowed a tough response to the killing. "Hamas will pay a heavy price for this terror attack," he said.
The boy was the first juvenile causality on the Israeli side since Israel embarked on the operation "Defence Edge" in Gaza. Of the 68 Israelis killed since then, 64 were soldiers.
Israel and Hamas resumed the fighting after the indirect negotiations in Cairo, aiming at achieving ceasefire in the hostility which began July 8, collapsed Tuesday.