Hi there I'm a speech and language therapist

I was recently reading an article about the optional infnitive account of child's language. This account seems to explain why children use accusatives in the subject position and non-finite verb forms within the same clause. However I have a child on my case load who will do this but also say utterances such as "he want to go home" in which the nominative case is correctly applied to the subject position which is what would occur if the T constituent was finite, however he incorrectly uses the infinitive form.

Can anyone explain to me what is happening here?