The NSW Registry of Births, Deaths and Marriages, has an index which is available online
http://www.bdm.nsw.gov.au/Pages/family-history/family-history.aspx
Has 5 children for James and Lucy Stevens - William Henry, birth registered 1878 at Sydney District; Frances H, registered 1880 at Balmain; James, 1882, Balmain; Ernest E. 1884, Balmain; Claude A, 1888, Balmain.
There is a death and funeral notice for Lucy Jane Stevens in The Sydney Morning Herald of Friday 30 May 1930. Found via Trove
http://trove.nla.gov.au/newspaper
The death notice names, husband James (deceased) and William, Annie, James, Ernest and Claude. (Annie presumably is a family name for Frances?)
The funeral notice, names Mr William Stevens, Mr and Mrs E. Childs, Mr and Mrs James Stevens, Mr and Mrs E Stevens, Mr and Mrs C Stevens, Mr and Mrs J Mackie and Mr E Childs and Families (the last two might be grandchildren and Frances or Annie probably married a Mr Childs)
With a combination of the NSW Registry and Trove you may be able to trace the family further.
Another good source to try and track more recent deaths is the Ryerson Index
http://www.ryersonindex.org/ and CoraWeb has links to a lot of Australian genealogy and historical sites
http://www.coraweb.com.au/
Hope that gets you started.