A child is ready for music therapy as soon as she or he shows a positive response to music. I once worked with an 8-month-old girl who had global developmental delays and I would play the guitar to encourage her to make sounds. When she started making sounds, I figured out what pitch she was producing, adapted the key I was in to match this pitch and used it in a song. It led to an increase in her vocal development which was one of her therapeutic goals.