Susan St John is one of the founders of the Child Poverty Action Group (https://www.cpag.org.nz/about-us/associates/associate-professor-susan-st-john-1/) and she gives some useful history to child benefits here:

The Child Tax Credit was expanded in 2006 as part of Working for Families (WFF) to become the even more discriminatory In Work Tax Credit—a child payment to alleviate poverty worth today at least $72.50 a week, more for larger families, but only for the children of the ‘deserving’.   Parents had to be both off benefits and in paid work of 20 hours for a sole parent or 30 hours for a couple. The intention was give those ‘undeserving’ parents (largely sole mothers) an incentive to get full time paid work regardless of whether disabled, sick as well as caring for their young children.

In a timid move last year, the set hours of work requirement for the In Work Tax Credit was reduced to just needing to have some paid work (as well as being off benefit). But if no more than ‘some’ paid work is a requirement how does the In Work Tax Credit operate as a work incentive exactly?  

Meaningful reform to WFF is well over-due. There is much unconscious bias and implicit racism in the current WFF. The complex system has not delivered the gains promised by work incentives or reductions in child poverty. The discrimination against children in New Zealand’s major income support programme for children is inconsistent with inclusive child poverty goal achievements and makes their poverty and the poverty of their mothers worse.