overseas nurse wanting to work in the mental health field

i'm about to qualify in NZ as a state registered comprehensive nurse with my Bachelor of Health Science (equivalent to US BSN I think?) I'm told to work in the US I have to sit the NCLEX exams - and I understand this bit, However, what I would like to know is, will this allow me to work in the field of Mental Health/Family Therapy? Here in NZ I have a position as a Child and Family Therapist in a community based, non-residential (i.e. out-patient) clinic. I obtained this position because of my experience and previous mental health qualifications. My question is - if I sit and pass the NCLEX, will this allow me to do similarly in the States? Would appreciate any help, advice or suggestions offered. Thanks