NZ privacy laws prevent 'official' information being available for possible living people. The children would be difficult to trace (not impossible).
Sidney & wife are buried in Bulls. Their headstones reveal names of children.
Cross check these names against available New Zealand Electoral Rolls using Sidney's name as search criteria and you will find the family farming in the Waikato 1960s-1980's. Both the sons' full names are available but I could not find the daughter.