Unprecedented numbers of small babies are in the care of unqualified home-based carers, as the Children's Commissioner investigates early childhood services.

The Commissioner, John Angus, is to report in February on which types of childcare are providing the safest and most nurturing environments.

He is likely to recommend an increase to the 14 weeks' paid parental leave to which mothers are entitled.

His inquiry coincides with a court charge against home-based carer Rachel Simons, of home-care service Porse, who admitted to the Herald on Sunday last week that she left a 4-month-old boy alone in Te Atatu all morning while she took her own child to the doctor.

According to Education Ministry figures, 8704 babies under 12 months old were enrolled in licensed services, a 30 per cent increase on five years ago.

Numbers of 1- to 4-year-olds in care have also gone up due to a baby boom from 2007 onwards, but not at the same rapid rates.

Home-based care has seen the biggest growth - up 74 per cent since 2006 - and this option is especially popular among parents of babies.

Other mothers, home anyway looking after their children, usually provide home-based care, taking in neighbourhood children to earn money. They do not have to have qualifications.

Angus said babies' needs differed vastly from toddlers. The latter benefited from social interaction and learning counting, reading and writing, the sort of interaction and education that can be provided at childcare centres.

But babies had particular developmental needs and were "particularly vulnerable", he said, and needed close attention from one or two carers. Angus said he was concerned most about babies spending 40 to 50 hours in care each week.

He said literature on the issue was "contentious" and it was an important area to investigate so he could inform parents on how to best choose childcare.

Angus was pleased some carers had set their own boundaries about restricting the hours babies were in care. "There are particular health and safety issues when looking after infants," he said.

Dr Sarah Farquhar, an early-education expert and director of website ChildForum, said there were "good and bad" carers in both centres and home-based services and parents needed to choose wisely.

She said even if parents trusted their carer they should do random checks to ensure they were doing what they claimed.

"Babies can't speak up for themselves and tell mum and dad what's happening during the day," she said. "Parents need to find out."

Childcare-centre and home-care operators were predictably split on which was safest.

Kidicorp owner Wayne Wright, who has about 100 centres nationwide including Topkidz and Mainly Kids, said childcare centres had more staff, and they were highly qualified, so were safer and better than home-based care.

But Jenny Yule, the managing director of Porse which is the country's biggest home-care service provider, argued they had an average ratio of only two children per carer, providing one-on-one attention.

Yule said Simons, who left a 4-month-old baby alone in Auckland this month, was a lone case in the organisation's 16-year history. They had 5000 Porse kids being lovingly cared for, she said.

The Children's Commission report is expected to recommend parents get more paid parental leave: the 14 weeks paid to New Zealand mums is less than in many other developed nations.

In the meantime, Angus urged parents to use "quality care" - whether in a centre or someone's home - and not to leave babies too long.