The family was working in their olive grove in the village of Helta, near the border with Israel, when the device exploded. The young boy died on his way to hospital and his brother was in a serious condition, medics said.
At least 22 people, including several children, have been killed by unexploded Israeli bombs in southern Lebanon since the Israeli war on the Lebanese movement Hizbullah ended with a UN-brokered cease-fire on August 14.
Explosions of Israeli cluster munitions in southern Lebanon -- mainly bomblets as small as a torch battery -- have also maimed more than 120 civilians, according to an AFP count based on UN figures.
The Lebanese army says that there are "possibly around one million" unexploded Israeli bomblets scattered around the south.

Copyright AFP (Agence France-Presse), 2006