A woman sold methamphetamine to an undercover officer as she breastfed her baby, police say.
The incident was part of a seven-month-long undercover operation by police, which investigated more than 100 drug-dealing homes across New Zealand in 2015 and 2016.
The operation focused on dealers supplying methamphetamine and cannabis.
Officers involved in the undercover operation infiltrated criminal gangs, and two separate gang chapter presidents were among those arrested.
Police said 40 children were found to be living in drug-dealing houses, and some of those cases have been referred to Child, Youth and Family.
Another woman sold drugs with a young child in her arms, said police.
Detective Inspector Craig Scott said more than half of the 155 people charged as a result of the operation had previously been linked to family violence incidents.
He said police were looking at what part drugs played in family violence.
"It's a complex area but we think that taking drugs obviously alters the mind and causes people to do things that they might regret, as well as consuming the family budget."
Detective Inspector Scott said the names of 40 children found to be living in drug-dealing houses have been sent their names to Child Youth and Family.