The blast occurred in Shakai, 25km north of Wana, the main town in South Waziristan region. The children, all aged between five and eight, were on their way to school.
Local officials suspect that the mine was planted by tribal militants supporting al-Qaida and Afghanistant's Taliban fighters, and was intended for security vehicles.
Militants also launched rockets at the airport at Miranshah, North Waziristan's main town, late on Sunday, a security source said. He said that no one was hurt in the attack. Troops retaliated by shelling suspected militant positions in the surrounding mountains, but there were no reports of rebel casualties either.
Pakistan, an ally in the US-led "war on terror," has deployed 80,000 troops along its border with Afghanistan to hunt al-Qaida and Taliban militants who fled into Pakistan's semi-autonomous tribal regions after the Taliban government was toppled in 2001.
The troops have captured or killed hundreds of suspected al-Qaida members over the past four years, but Afghan officials often complain that Islamist militants, particularly Taliban fighters, attack Afghanistan from bases in Pakistan.
About 200 tribesmen were killed in fighting with the army in North Waziristan this month when they answered a call to arms by militant Muslim clerics after a special forces assault on an al-Qaida camp.
On Thursday Pervez Musharraf, Pakistan's president, warned foreign militants hiding in the tribal region to leave Pakistan or die.