Music therapy and learning to play an instrument are not the same things. And while they may have some overlapping benefits, the overall goals and techniques used are not the same.
If you are looking to build your child’s vocal skills or have them learn to play an instrument you would need to find a musical instructor, not a music therapist. However, with that being said, playing an instrument can be part of the therapy process, but learning to play the instrument is not the priority.