Major Ali al-Shahrani, civil defence spokesperson in southwest Saudi Arabia, told reporters a nine-year-old brother of the boy was also wounded when a Katyusha rocket his their family’s home.
The attack came a day after rockets fired from Yemen struck a power station in Najran, marking a rare hit on Saudi Arabia’s infrastructure after months of periodic bombardment of the area.
Attacks have intensified since the suspension in early August of UN-brokered peace talks between the Shia Huthi rebels and their allies, and Yemen’s internationally-recognised government which has the military support of a Saudi-led Arab coalition.
Ten people have been killed in Najran since August 16, when a single strike claimed seven lives.
The Arab coalition has also stepped up its air raids in Yemen since the peace talks collapsed.
The coalition intervened in March last year to support President Abedrabbo Mansour Hadi after the Huthis and their allies seized much of Yemen.