How do I find if they had any children
The NSW BDM death certificate (or an official transcription) includes sections that address the following:
The surname and given names of the deceased and
sex and age,
the date of death,
the place of death
the usual place of residence,
the usual occupation
the marital status at death
The details of any marriage/s
Where and when married, and age when married, and the full name of the spouse (former and maiden names)
If more than one marriage, then the following details are listed under each marriage
the names of thethen living children of the marriage, with their ages, and the gender (sometimes their names) of any children of the marriage who were no longer living
The details about the deceased Parents (father's given names and family name and mother's given and former and maiden name
MOST of the above information comes from the 'Informant" whose name, address and relationship to the deceased is stated on the registration
Then there's the Medico's section providing the information about:
Cause/s of death and duration of last illness
Then there's the funeral director's section and sometimes this will include the clergy details too,
Advising if a Burial or cremation, the date and place of internment.
NSW BDM gives #28469 for Archibald Duncan NIXON's 1953 reference.
RChat's link re Official Transcription Agents
http://www.rootschat.com/forum/index.php/topic,300394.0.htmlArchibald Nixon:
Death notice: http://trove.nla.gov.au/ndp/del/article/18396047?
Funeral notice: Randwick General Cemetery http://trove.nla.gov.au/ndp/del/article/27523228?
cheers 
cupoflife
Cheers, JM