Female prisoners are allowed to keep their babies with them behind bars for more than twice as long as before, under a law change introduced this week.
But infant welfare specialists are torn over whether the increase, up to two years of age, is a good move, with groups arguing the changes will make children insecure and anxious.
Specialist mother and baby units will open women's prisons in Auckland and Christchurch women's on Monday, allowing inmates to live with their babies beyond the current age of nine months.
Infant mental health specialist Kate Dent Rennie said it was "inhumane" to separate a child from its mother at two, so it was better that the child is raised by another caregiver altogether.
"It's a very deep heartbreak for a two-year-old to lose the one main person in their life and it has development consequences associated with it that we know very, very well," Ms Dent Rennie told Radio New Zealand.
"The loss of a primary caregiver at the age of two is going to put that child in a very anxious and difficult state for being able to feel secure in the world."
However, Plunket clinical adviser Allison Jamieson argued the opposite, saying the age should be increased to at least three.
"Babies and mothers need to be together," she said.
"There is that attachment and bonding that needs to happen and if mothers and babies are separated that's never going to happen."
She said the first three years of a child's life are the most important because that is when all the connections are formed.
The New Zealand College of Midwives applauded the Ministry of Justice move and said the focus should be on ensuring babies and mothers are allowed to continue building their bond after separation.
NZN