I would think that clearly, not all had wives and children. You must also factor in the number of children, women, both married and unmarried as well as those men too old for battle. Even if the number of children was a conservative ratio of two to one, that is still going to be in excess of 1.5 million. Based on the various numberings of the people in Numbers, I would think the number of Israelites alone would be between 1.5 and 2.5 mil I am certainly not adamant about the number 3 mil. but, I think it is probably close to the size of the camp.