Chinese tourist visa for Pakistani family in Moscow..

Hi, we (my wife, 1 year old son and I) are Pakistani citizens, I am working in Tula region in Russia (have a three year Russian work permit) and we would like to go in Oct/Nov to China for a week of vacations. Could you please let me know if we can get the visa in Moscow, what are the requirements. what would be the expected time to get the visa and do we need "Valid Invitation Letter offered by a travel agency that is authorized by Chinese Government"? Our idea was to do like a simple vacation based on our pace not one strereotype designed by agency...