Mark's answer gives the link to Online BDM records for Victoria.
Department of Justice, Victoria, Australia - BDM Online [ https://online.justice.vic.gov.au/bdm/indexsearch.doj
Using that site, you should find at least six children (birth years and reference numbers below):
Alma Kingcott Hayes - 1903/3049
William Hayes - 1904/17908
Henry Archibald Leonard Hayes - 1907/1007
Chloris Grace Hayes - 1909/19007
Muriel Estella Hayes - 1913/15315
Alexander Hayes - 1916/27841
There could be more children born after 1916 (cut-off date for birth records).
Beware of abbreviations! Victorian Indexes use abbreviated names with absolutely no logic, so you may need to try various spellings when searching for other names.
Alma's middle name at birth was Josephine but appears elsewhere as Josine. Alma and William were married in 1901 (reference no.8311)
William Leonard Hayes was the son of Henry Hayes and Eliza Jane Kingcott.