(1) Each county having a population of less than 750,000 shall provide child welfare services through its county department.
(2) Each county department shall employ personnel who devote all or part of their time to child welfare services. Whenever possible, these personnel shall be social workers, as defined in s. 457.01 (10).
(3) This section shall not apply to those counties which had child welfare services administered by the staff of the juvenile court prior to January 1, 1955.