Before proceeding, check over this chart to see if your son needs to file. Further instructions are below the chart. Also, inmates are not eligible for the Earned Income Credit or Child Tax Credit.
https://ttlc.intuit.com/replies/3302274
Yes, you can. However, you must have a power of attorney to be able
to take care of his tax issues. Your son must file Form 2848 with
the IRS- it will authorize you to deal with his taxes. Good luck in this process.
Here is the form and it's instructions:
https://www.irs.gov/pub/irs-pdf/f2848.pdf
https://www.irs.gov/pub/irs-pdf/i2848.pdf
