The purpose of this study was to examine the differences in ethical beliefs and management skills according to developmental levels of music therapists working for children. The collected data from randomly sampled 83 professional Korean music therapists working for children were divided into two groups based on their development levels, and then the t-test of the independent sample was conducted to address the research purpose. First, this study found that there were statistically significant differences between the suitability and efficiency of therapy and the ability of the counsellors for children among the subordinate categories of ethical belief, depending on the developmental a level of professional music therapists for children. Second, the study indicated that there were statistically significant differences in structuralization of therapeutic relationship, ability of the counsellor for children, confidentiality and privacy protection, depending on the development level of music therapists for children. This result showed that the therapists in the group with high development level have relatively right ethical beliefs, compared to the other group, and properly manage ethical issues such as structuralization of therapeutic relationship, ability, and confidentiality and privacy protection for the clients. This study provides basic information on directions of ethical education in the training program for music therapists.