The Children's Commissioner's Expert Advisory Group on child poverty recommended a universal child payment, like the old family benefit, but the MPs said government couldn't afford to pay right through each childhood.
Labour decided the first year was the most important time. Most families lost income in that year, either through working less or through paying more for child care, the MPs said.
The Best Start policy would extend the payment to families earning less than $50,000 a year until the child was 3 years old.
The package also includes increasing free early childhood education from 20 to 25 hours a week for children aged 3 to 5, increasing the number of early childhood centres and having all their staff fully qualified.
The party also wants to increase paid parental leave from 14 to 26 weeks as recommended by the World Health Organisation.
Labour is also looking to beef up medical and welfare support for pregnant women and babies.
Best Start has been costed at $530 million a year and could be fully implemented in 2018.
The MPs said the money would come from cancelled parts of Labour's fiscal package, and also from GST and a new top tax rate rate that has yet to be announced.
"We will preside over a strengthening economy too, but we have a plan to make sure benefits are spread to a whole range of people."
Children who have a poor start in life cost the country $6 billion in areas such as remedial reading and avoidable hospitalisations, Ms Ardern said.
There are an estimated 50,000 New Zealand children under 3 years old who are living in poverty. Ms Arden defined that as living on 60 per cent or less of the median income.
In the Wanganui District 60 per cent of the median income per person per year at the 2013 Census was just over $14,000.
People on less may not be able to eat three meals a day, see a doctor when they need to or send their children on school trips.