You say you found a fit in 1891 with a son of a William and Sarah.
However you may wish to look also at William J Randall 8 months old in 1891, son of Henry/Harry? T Randall and Sarah, at 192 Seven Rd, Bromley by Bow. RG12/328/88/66. (Rendell on Anc).
Birth reg as William John Randall, mmn Stone, Sep qtr 1890 Poplar.
Parents' marriage: Henry Thomas Randall and Sarah Stone, Jun qtr 1883 Poplar.