Section 62B. In each such city and town there shall be an unpaid commission, called the commission on children's health camps, to consist of the mayor or chairman of the board of selectmen, who shall have no vote, the superintendent of schools, the members of the board of health, all to serve ex officiis, and also seven residents of such city or town to be appointed by the mayor or the chairman of the board of selectmen. One member of said board shall be designated as chairman by the mayor or the chairman of the board of selectmen. Of the seven persons first appointed after such acceptance, two shall be appointed for terms of one year each, two for terms of two years each, and three for terms of three years each, and thereafter as the term of each member expires his successor shall be appointed for the term of three years. Each appointment made to fill a vacancy in said commission shall be for the balance of the unexpired term.