A plate of food at the tent being operated by the prestigious Windsor Hotel was selling for $7 in a country where many live on less than $2 a day.
'Hawkers allowed'
The children, who had been begging for food, launched the raid after being told they would have to pay for the food.
The hotel management declined to comment on the incident.
Two days ago, World Social Forum organisers were forced to waive entry fees for participants after Nairobi slum dwellers staged a demonstration against the charges.
Participants were originally being asked to pay a 500 Kenyan shillings ($7) accreditation fee.
"We are now not charging anybody, the event is free so that many people can participate," Boniface Beti, the event's media officer, told the BBC.
Mr Beti also said hawkers had recently been allowed in to sell cheap food to participants as up until a few days ago five-star catering firms had dominated business.
Tens of thousands of people are attending the World Social Forum, which is being held at the same time as the World Economic Forum - hosted in the Swiss town of Davos.
At Davos, the world's largest corporations are discussing business and hammering out trade deals, while the Kenyan event is addressing a wide spectrum of the world's social problems - including poverty.
