Here is the marriage of Thelma Josephine Adelaide TREVAN, on the 24.11.1924 at Presbyterian Church Whyalla, to Stanley Samuel James PARKER, aged 25, son of Samuel James Parker. Bride was aged 21, father Frederick.
They had the 2 children that I could find,
Stanley Frederick James PARKER b. 17.8.1925 Pt Pirie
Dorothy Ella PARKER b. 14.8.1927 Pt Pirie
SA birth records finish at 1928 on disc.
There is also a Ida Caroline May TREVAN, married at the same place on the 10th August, 1920, aged 20, father Frederick. Her groom, James Roy Reynold or Randolph BILLING, aged 21, son of William Billing.
Found these children:-
Valma Merle BILLING b. 7.11.1920 at Whyalla
Roy Frederick BILLING b. 18.8.1922 at Whyalla
Hope that helps a little more - Sashar