In a wind instrument the variation is by the airflow and the length of the column of vibrating air. In speech, as well as adjusting for pitch, we can adjust the shape of the column, the size of the resonator, and whether or not the vocal cords are vibrating. More adjustment than with any instrument. We think of vowels and consonants. But we adjust the muscles according to the sounds we want – as though there were keys for each adjustment.
The best help that I can give you and your child is by applying the science of speech and language, known as linguistics. Why does your child have the problem which he or she does? And how does this fit into the problems which children have more generally?
From my experience, research, and reading of the literature, I believe that the learner’s task, looked at generally, is not about words and sentences, but POSSIBLE words and sentences. So the clinical task is one of helping children discover how to build words and sentences as and when they want and enjoy story-telling and conversation.
While the role of the tongue and the lips in speech is obvious, one commonly neglected aspect of speech and language, there is also what is known as the rhythm or ‘prosody’, as in holly and hello, affecting every word in the language.