Their vehicle was raked with gunfire as they returned home from work at a children's community centre run by Pakistani charity Ujala, (Light), said district police officer Abdur Rashid Khan.
Their driver was seriously wounded in the attack. The motive for the shooting in Swabi district, about 75 km northwest of Islamabad, was not clear and no one at Ujala was immediately available for comment.
Last month gunmen killed nine health workers taking part in a national polio vaccination drive in a series of attacks. The Taliban said they did not carry out those attacks, although its leaders have repeatedly denounced the vaccination programme as a plot to sterilise people or spy on Muslims.
Aid workers have frequently been kidnapped or killed in Pakistan, a nuclear-armed nation of 180 million that is struggling to contain a Taliban insurgency and plagued by endemic corruption and violent crime.