Are you looking for actual descendants or just tracking him through the censuses?
There's a death registered for a Francis J Walwyn, Mar qtr 1929 Aston. Age is given as 61.
Living with Mother and grandparents in 1871.
Living with parents in 1881 at 76 Vauxhall Road.
Living with Mother in 1891 at 76 Vauxhall Road.
Marries Florence Stokes Jun qtr 1891 Birmingham.
And other possibles...
Parents, John Eldershaw Walwyn and Mary Ann Mallin, marriage registered Jun qtr 1862 Madeley
Grandparents, Abraham Mallin and Emma Lane, married 7 June 1844 Birmingham.
Great Grandparents, William Mallin and Ann Rollason, married 3 Apr 1809 St Martin Birmingham.