Rod Stewart's "version" is not even the same song, Anthony (although it does crib bits and pieces of the original Dylan lyrics here and there). It just happens to have the same title. You cannot copyright a title. It also has, of course, the same general theme.

Dylan wrote the 1974 one specifically for his children. Rod Stewart's song was, I think, consciously directed at his entire audience. Mind you, in '74 Dylan's entire audience assumed that his song was directed at them. ;-)

The Rod Stewart one (from the late 80s?) was either a deliberate imitation of Dylan's 1974 song...or it was a subliminal imitation of it. The music is all different. The verse arrangements are very different. The Chorus (if you could even call it a chorus) is totally different. The lyrics sound like a sort of half-assed attempt to copy the Dylan song without doing it totally obviously. You just grab a line here, a phrase there, throw them in a blender, spin them around along with some pages from a rhyming dictionary, and write down what comes out when you pour the resulting concoction on a fresh new sheet of paper.

Listen to both songs, look at when they were recorded, and you'll see what I mean.