The charges relate to the January 16 death of a 16-month-old, who died after he was left in a car in the Whanganui hospital car park on a hot day.

A woman has been charged with manslaughter in relation to the death of a toddler who was left in a car in the Whanganui Hospital car park.

Police had been conducting an inquiry into the January 16 death of the 16-month-old boy.

The woman, 35, appeared before Judge David Cameron in the Whanganui District Court on Thursday. She was granted interim name suppression.

She was remanded at large and will re-appear in the High Court at Whanganui on May 6.

The woman is a Whanganui District Health Board employee.

Board chief executive Julie Patterson said while the DHB understood the decision to lay charges, "we do feel for our colleague and we will continue to support her and her family through the challenging days ahead".

Patterson acknowledged the thoroughness of the police investigation and thanked police for their sensitive and thoughtful approach when interviewing DHB staff.

"Out of respect for our colleague, and especially given the court suppression orders, the WDHB will not be making any further comment."

Paediatric Society of New Zealand president Dr David Newman has previously spoken about the dangers of children being left in cars.

An outside temperature of just 21 degrees Celsius meant the inside temperature of a car could reach 49C in just 45 minutes as the sun radiated through the windows, he said.

"An adult could not survive in that heat and children are far more susceptible to it. They overheat three to five times faster than an adult."

Younger children have less surface area and fewer fluids, meaning their core body temperature heats up much faster than older children and adults.