Wow - very possibly they did move frequently. Floyd pops up in Chicago to be married in 1911, Oliver is born in Indiana in 1912. Vivian is born in Idaho in 1914. If they were in New York in 1915 (still checking) then he was in LA, California in 1917 for the WW I draft cards. Denver, Colorado in 1942 for the WW II draft cards.
Yep - in 1920 in Los Angeles - there are Oliver and Vivian.
"United States Census, 1920," database with images, FamilySearch(https://familysearch.org/ark:/61903/1:1:MHQD-KQT : accessed 2 November 2017), Floyd Hardin, Los Angeles Assembly District 61, Los Angeles, California, United States; citing ED 113, sheet 10A, line 29, family 235, NARA microfilm publication T625 (Washington D.C.: National Archives and Records Administration, 1992), roll 105; FHL microfilm 1,820,105.