Well, there's a Thomas Sheppard b 1835 Morden(Marden) Wilts, shepherd on a farm, in the 1901 Census with wife Agusta (it does say that on the image!) and son Sydney aged 21: RG13 Piece 1917 Folio 52 Page 12.
So Fanny took Alice and George, but left baby Sy(i)dney behind?

1891 RG12 Piece 1592 Folio 43 Page 4, Thomas is calling himself a widower:
Blue Vein, Box, Chippenham, Wiltshire
Thomas SHEPPARD Widr 57 Shepherd b Wilts Easton Royal
Frank Son 17 Farm labourer b Avebury
Bertha Dau 14 Housekeeper b Avebury
Sidney Son 11 Scholar b Easton Royal
Bertha appears to be registered as Bertha Ann SHEPPARD: Jun Qtr 1875 Marlborough Vol 5a Page 90; not Florence, unfortunately.