The story just goes on and on. Given the information from Garstonite about possible other children, I kept digging.
I found another daughter (it seems) named Ada Johnson Hargreaves b. 1896, died 1897
Then I went to the LANC OPC records and searched for Hargreaves and found the following:
Baptism: 31 Dec 1896 St John the Evangelist, Great Marsden, Lancashire, England
Ada Hargreaves - [Child] of Elizabeth Ann Hargreaves
Born: 11 Mar 1896
Abode: 1 Yorkshire St
Notes: Privately [in margin. Father's details blank]
Baptised by: A. Wilson
Register: Baptisms 1895 - 1899, Page 37, Entry 296
Source: LDS Film 1471098
Baptism: 31 Dec 1896 St John the Evangelist, Great Marsden, Lancashire, England
Fred Hargreaves - [Child] of Elizabeth Ann Hargreaves
Born: 18 Sep 1893
Abode: 1 Yorkshire St
Notes: Privately [in margin. Father's details blank]
Baptised by: A. Wilson
Register: Baptisms 1895 - 1899, Page 37, Entry 295
Source: LDS Film 1471098
Baptism: 31 Dec 1896 St John the Evangelist, Great Marsden, Lancashire, England
Sarah Hargreaves - [Child] of Elizabeth Ann Hargreaves
Born: 18 Oct 1889
Abode: 1 Yorkshire St
Notes: Privately [in margin. Father's details blank]
Baptised by: A. Wilson
Register: Baptisms 1895 - 1899, Page 37, Entry 294
Source: LDS Film 1471098
Burial: 9 Jan 1897 St John the Evangelist, Great Marsden, Lancashire, England
Ada Johnson Hargreaves -
Age: 9 months
Abode: 1 Yorkshire St. Little Marsden
Buried by: George A Fry
Register: Burials 1895 - 1900, Page 50, Entry 399
Source: LDS Film 1471098
It looks as if little Ada was ill and mum took two of the others along to be baptized as well. This makes it look like 9 children altogether.
Still looking for John Hargreaves' death. Perhaps the marriage cert will give me his father's name, which will help weed him out from all the other John Hargreaves (please let it be Hubert or Aloysius).