Not sure how well you know that part of the world but it seems they have roots on both sides of the river Trent, Owston Ferry being on the west (Sheffield) side.
Just to confirm the 1911 for Amy should read as Keadby but perhaps she was born in a small village between there and Owston Ferry
birth: 16 August 1906
christening: 20 August 1906 Althorpe, Lincoln, England
parents: Thomas Duffield, Maud
And Reginald in the 1911 does look to be the 1900 Arthur Reginald in the bmd
Arthur Reginald Duffield
christening: 14 January 1900 Owston, Lincoln, England
parents: Thomas Duffield, Maud
Still missing a youngster according to that 1911, 4 born and still living in 1911 (but it appears there are only 3 on the census return) plus Thomas in 1915.