A couple who were high on synthetic cannabis, in a vegetative state, while their baby was strapped in a stroller on a hot summer afternoon, have been jailed.

The couple, who can not be named in order to protect the child's identity, appeared in the Rotorua District Court before Judge Greg Hollister-Jones today to be sentenced on a charge of neglect of a child.

The offending happened on the corner of Fenton and Pukuatua Sts in January this year.

The man was also sentenced on a charge of assault with intent to injure after head-butting his partner in April.

The pair were sentenced separately as the woman was the victim of the assault.

She held back tears as Judge Hollister-Jones described the offending.

"This was a hot summer afternoon ... you had the child with you strapped into a stroller and dressed in a heavy sweatshirt and a blanket.

"You were in a coma after consuming synthetic cannabis.

"Passersby became concerned about your state and child being exposed to direct sun. Both you and your co-offender were found to be in a vacant and vegetative state and unresponsive initially."

The judge said when police removed the child from the situation, the couple didn't even realise.

He described the almost 2-year-old as vulnerable as she was unable to remove herself from direct sunlight and said she was found with insect bites and open sores on her body.

"There was a breach of trust. You're a mother, you're there to protect and take care of her," he told the woman.

"I'm grateful for your acknowledgement of the harm you caused on this day and the dereliction of duty as a parent. It's completely unacceptable for parents who have the care of a vulnerable infant to be completely intoxicated on an illicit substance."

He told the man "you were intoxicated, and grossly so".

Judge Hollister-Jones acknowledged the woman was now sober and in the process of rehabilitation and sentenced her to 10 months' imprisonment with six months' post-release conditions.

The father's lawyer, Tim Braithwaite, said the man acknowledged he had put himself before his baby.

In relation to the man's assault charge, Judge Hollister-Jones said that had physical and emotional effects on the woman.

"You were out with your partner [in April 2018] you became angry and head butted her in the forehead with enough force to make her fall to the ground. You stood over her and told her to 'eff off'."

The man was sentenced to one year and seven months' imprisonment made up of 12 months for the neglect charge and seven for the assault.

He was ordered to serve two months concurrently for a breach of release conditions.