The first Robathan births, mother's maiden name Riches, seem to appear in 1913?
1911 has an Enid Riches of the right age - are you sure she married in 1902?
December qtr 1913
Cardiff district vol 11a, page 704
Robathan, Denis P
Cardiff district vol 11a, page 705
Robathan, Francis E
June qtr 1915
Cardiff district vol 11a, page 832
Robathan, Elizabeth D
June qtr 1920
Cardiff district vol 11a, page 864
Robathan, Carlton G B