Police said Harrison and Marsh had been drinking with friends at their Te Puia Springs home on the night before baby Elray died.
Elray was put in his cot that night, but the next morning Marsh put him in bed with Harrison before he went to work.
This was normal practice for the couple.
When Harrison woke up around 8am she found baby Elray lying face down on her chest and not breathing.
Harrison told police she had drunk a box of Steinlager during the night and did not know what time she went to bed. She did not recall her partner putting the baby in bed with her the next morning.
After the sentencing, Detective Senior Sergeant Dave Greig of the Eastern District Police Child Protection Team said the circumstances of baby Elray's death were of significant concern to police and other agencies.
``The dangers of babies co-sleeping with parents, and in particular parents who have been drinking, are well-known and health agencies are continually trying to educate families about the issue.
"In this case, the information provided to the parents by health professionals prior to and after the death of baby Kasey in 2010 was ignored and they failed to change their lifestyle or their habits during the care of Elray,'' Mr Greig said.
The couple's actions were difficult to comprehend given the level of information that had been provided to them prior to Elray's death in relation to safe sleeping practices.
"As parents we have social and legal obligations to ensure the safety of our children, including making sure that we provide a safe sleeping environment for them.
"In situations such as these where there is a significant departure from the standard of care expected of parents, then criminal charges will be considered.''
Police and other agencies treated these cases very seriously and in this instance an extensive investigation had been undertaken by the Eastern District Child Protection Team, and independent legal advice had been sought prior to the charges being laid, Mr Greig said.
Co-sleeping has been identified as a major factor in SUDI deaths. Health agencies discourage it due to the risks it poses for babies.
