This comes as the governor pledges to cater for funeral expenses of the seven pupils who died after a class collapsed.
A communication official at City Hall said Nairobi County officials who inspected the school will be fired and charged in court.
Sonko had travelled to the US to attend the United Nations General Assembly where, for just one week every September, the headquarters hosts everyone from kings, presidents and prime ministers.
Sixty-eight of the 70 Precious Talent School pupils who were admitted to Kenyatta National Hospital were discharged.
The two others are still at the hospital, with one in the intensive care unit.