An L-2 spouse is employment-authorized incident to status, so no separate work permit is needed to be allowed to work. Practising as a dental hygienist also requires the state's professional licence, which is a separate matter from immigration permission.
Immigration permission is not a professional licence
Hypothetical example: the manager's spouse holds a New Brunswick dental hygiene registration. Once admitted in L-2 status as the spouse of an L-1A manager, she is authorized to work incident to that status, and her admission record can serve as evidence of that authorization for an employer. Whether she can practise dental hygiene depends on the destination state's licensing board, which may require an examination, a credential review or a jurisprudence test before she can accept a clinical position. Sequence the state licence application early, because that process is usually the slower one. Children admitted in L-2 status may attend school but are not employment-authorized on the basis of their derivative status. Each family member's own activity determines whether any further step is needed.
Hypothetical example: a ceramic-restoration teacher accompanying an L-1A transferee wants to begin paid classes soon after arrival. A qualifying L-2 spouse has work authorization that comes with valid L-2 status, but the person should retain the admission record and current status evidence an employer will request. The child’s situation is different: an unmarried child under 21 in L-2 status can attend school but cannot take employment. Make a household table with each person’s passport nationality, date of birth, intended activity, and required visa steps. That table identifies whether a child is close to the age limit or whether a spouse needs a professional licence before accepting a job. Do not use the principal's transfer letter as proof of every family member's eligibility.