Play video content EXCLUSIVE TMZ.com

William H. Macy's paternal concerns aren't limited to his real life kids -- he also cares deeply about Ethan Cutkosky, his TV spawn who just got busted for DUI.

We asked the "Shameless" dad about Ethan's arrest, and he immediately went to bat for the 18-year-old ... telling us he's a good kid. He also had sympathy for child actors who have to grow up in Hollywood.

He was rushing into LAX when we talked to him, but William said he plans to take some time to call Ethan, and possibly offer some fatherly advice. In other words ... the exact opposite of how Bill's Frank Gallagher character would react on the hit Showtime series.