Benjamin died in Tasmania in 1888.
His obit states no children.
There are a number of articles about Benjamin on Trove.
http://trove.nla.gov.au/

His (and Charlotte's) will is online at
http://prov.vic.gov.au/research/wills-and-probate

No mention of children. Mentions/names children of his siblings.

Australia Death Index, 1787-1985
Name: Benjamin Hepburn
Death Date: 20 Feb 1888
Death Place: Tasmania
Age: 62
Registration Year: 1888
Registration Place: Launceston, Tasmania
Registration number: 87
Estimated Birth Year: abt 1826
Buried Smeaton Victoria.

Australia Marriage Index, 1788-1950
Name: Benjamin Hepburn
Spouse Name: Charlotte Ellen Bassano
Marriage Place: Victoria
Registration Place: Victoria
Registration Year: 1854
Registration number: 326