They included the director of WCK’s kitchens in Gaza, the agency added.
Pictures circulating on social media showed a white saloon car by the side of a road, partially burned-out and with its roof caved in.
Video filmed inside a mortuary also showed a number of charred possessions – including a laptop, clothing, and and ID badge – bearing the WCK logo.
Separately, British aid agency Save the Children said one of its staff members was also killed on Saturday afternoon in Khan Younis.
Ahmad Faisal Isleem Al-Qadi, 39, had been returning home to his wife and three-year-old daughter from a mosque when he was killed, the charity added.
“Ahmad, who was deaf, will be remembered for his determination to help others, for his pride in his daughter, and for his ability to brighten others’ days”, Save the Children said in a statement.
It is unclear whether he was killed in the same strike as the WCK employees.
Also on Saturday, medics said at least nine people were killed when an air strike hit a car near a group of people who had gathered to receive flour, according to Reuters.
A doctor who told the BBC he had treated people injured at a food distribution point said he would not have “appreciated the magnitude of injury and death” had he not seen it for himself.
“I operated on a man with shrapnel injury with no fewer than nine holes in his bowels. Others had much worse injuries.”
He said that even many doctors were now having to survive on food handed out by aid agencies.