Can I file my son's taxes for him

[avongrant1679]

He's in prison I run his llc for him

[Opus 17]

Yes.

Technically you should get a power of attorney, the IRS has their own form that gives POA for tax returns only.

https://www.irs.gov/forms-pubs/about-form-2848

As a practical matter, if you e-file and he agrees with what you are doing, you can probably get away without the POA form, but I think it would be better to have it so everything is clear.