The 1891 census has Fred & Emma living with Freds parents and 2 children Frederick and Jessy. The original does look like Jessy but could also possibly be Lilly:
"Jessy" is enumerated as a 3 yr old girl (born Stepney) but I think that the child was in fact a son of Emma's first marriage.
Marriage of Emma Knox to Jesse Mills: Dec qtr 1887 Bethnal Green.
Birth reg of Jesse William Mills, mmn Knox: Sep qtr 1888 Mile End Old Town.
Emma's husband's possible death: Jesse Mills aged 21, Sep qtr 1888 Mile End**
**Added: The deaths register of the Mile End Old Town Infirmary shows that Jesse died on 14 June 1888 aged 21 - cause of death Morbus Cordis.