You can prepare and file the return for him if you file IRS form 56 "Notice concerning fiduciary relationship" as that will appoint you as the personal representative of your son. This form will allow you to legally sign the return.
You can find the form here:
https://www.irs.gov/pub/irs-pdf/f56.pdf
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"
