As John/Phillip was not yet 3, and was, apparently, one of 6 children when his parents separated perhaps-speculation only - there was some kind of foster/adoption arrangement with the surname Scott.
According to the online tree I mentioned earlier, which appears to be well-researched, Benjamin Butler later lived with and had 4 children by Nellie Carlyle Hard. (Unable to verify these births as birth records only allowed earlier than 100 years ago)
Seems to be supported by this:
Electoral Rolls
1931 Benjamin Butler, labourer, Nellie Carlyle Butler, home duties, at 423 Armstrong St S, Ballarat West
Edit to add: one of the children listed to Benjamin Butler and Nellie is Jean Douglas BUTLER, later Jean Douglas Villarroya whose death shows her parents:
Death, Victoria, 1969 #28961
Jean Douglas Villarroya
Father Benjamin Butter (sic)
Mother Nellie Carlyle Hard
Judith