The department shall deny a private adoption agency a license, or revoke an existing private adoption agency license, unless the applicant or licensee demonstrates that it currently and continuously employs either an executive director or a supervisor who has had at least five years of full-time social work employment in the field of child welfare as described in Chapter 5 (commencing with Section 16500) of Part 4 of Division 9 of the Welfare and Institutions Code or Division 13 (commencing with Section 8500) of the Family Code, two years of which shall have been spent performing adoption social work services in either the department or a licensed California adoption agency.