He thought a manslaughter charge shouldn't apply when extreme violence was inflicted on babies and toddlers.
"Children are vulnerable. To argue that injury or death was not intentional, so therefore murder can't be applied ... it doesn't do justice."
McCoskrie said in this case, the parents were told of the dangers of shaking a baby.
"They knew they couldn't shake a baby.
"When dealing with children and babies, you should be able to foresee shaking or treating a baby or toddler roughly or with violence could result in injury or death," he said.
He said it was clear Child Youth and Family (CYF) had high concerns for the twins when they were discharged from the special-care baby unit.
"To me, this shows the whole issue of when the red flags are raised and when it is clear these are the ones we need to put time and resources into."
He said it didn't matter whether the act of violence was just one-off or over a long period of time.
Anti-child abuse advocate and creator of the Facebook page 'STOP Death and Abuse of our Children' Cherie Kurarangi said today's sentencing was "more than too light".
"There is too much tolerance for the way our babies are treated.
"We know he was a young dad but where was that recognition when she was alive?
"One thing I'm struggling with as well, with every single [child abuse] case is they need a range of support to manage the dysfunctions going on and the stress levels in their lives."
Kurarangi said Wichman could have asked for help earlier.
"Nark on yourself. Say it before you do it and we might be able to help."
New Zealanders shouldn't be just relying on government organisation CYF -- communities should help and support struggling families.
"We can't just rely on one agency we can all do something.
"It takes a village to raise a family."
Child Youth and Family Regional central director Karen Hocking confirmed the family were known to the agency.
"Given the premature birth of the twins, considerable support was wrapped around the young parents to help them manage their babies," she said in a statement.
"Before the twins were discharged from hospital a plan was worked out to ensure a family member was in the home to provide extra support and monitoring.
"After they were discharged, CYF made several home visits.
"The parents appeared to be managing well and had a lot of support from both their extended families and from community agencies. Child, Youth and Family had no ongoing involvement with the family at the time of Teegan's death.
"The Court has found Wichman responsible for Teegan's death and he is being held to account for that."
