Long-term family studies allow researchers to bank plenty of data for future use.
Then in five or 10 years' time, instead of asking people to remember what was the first solid food their children ate, they can simply peer into their computer and find that it was most commonly banana - at least for children born in 2009 or 2010 in Auckland or Waikato.
The banana finding, published today in a report by Auckland University's government-funded Growing Up in New Zealand longitudinal study team, may seem fairly predictable, but others came as a surprise to the researchers and are held to be important for policy-makers, such as that 32 per cent of families moved home between the two interviews when their children were 9 months old and when they were 2 years old.
The research involves repeated interviews with the mothers and their partners on physical, social and economic factors, such as the children's health, the family's use of child care, household crowding, income and how long the children use computers and TVs for each day.
An associate director of the study, Associate Professor Cameron Grant, said that when the children were 7 they would have their lung function tested.
"We will be able to work out what proportion of children have got good healthy lungs and good lung function and what proportion have already got significant problems with lung function."
The researchers would look back for correlations between lung disease and recorded factors, such as delayed vaccination, exposure to cigarette smoke during pregnancy and in infancy, poor housing and poor nutrition.
The report, based on the interviews at age 2, records an ethnicity mix of 71 per cent European, 24 per cent Maori, 20 per cent Pacific, 16 per cent Asian, and 3 per cent Middle Eastern, Latin American, African or other. Multiple ethnicities were indicated for 42 per cent. Overall, 35 per cent of the children had one sibling, 16 per cent had two, and 12 per cent had three or more.
Eighty-six per cent of children were reported to have excellent or very good health.
The first word spoken by 37 per cent was some version of "Mama", "Mum" or "Mummy", while "Dada", "Dad" or "Daddy" was first for 26 per cent. The average age of speaking their first word was 10 months, and of taking their first, wobbly steps was 12 months.
Families Commissioner Belinda Milnes highlighted the study's findings on changes in the number of women without a partner, from 212 in the pregnancy phase, to 439 at the 9-month interview and 319 at 2 years.
"These changes have important implications for the effectiveness of support systems for sole parents and their children.
"A future Growing Up in New Zealand report will focus on transitions in and out of vulnerability."
Mandarin's an easy fit for Lana
Auckland parents Joanne Ung, 37, and Young Lee, 35, speak Mandarin and English to their two children.
The couple, who met at Burnside High School in Christchurch, are originally from Cambodia and Malaysia and moved to New Zealand with their families in their early teens.
Although they speak a variety of Chinese dialects between them, they chose Mandarin for their children because it was the most logical option.
Their 5-year-old daughter, Lana, is part of the Growing Up in New Zealand study.
Forty per cent of children in the study were able to understand two or more languages at age 2.
"We look Chinese, so my husband wanted my kids to be able to speak Chinese [Mandarin] when a Chinese person comes to them," Ms Ung said.
Her husband's inability to speak Mandarin well also factored in the decision, Ms Ung said.
"We chose Mandarin because I can speak it quite well and it's quite commonly used - anywhere you go, within Asia, people will understand Mandarin."
Ms Ung, an accountant, said Lana and her older brother Zachary, 7, attended a Chinese school on Saturdays to help with their Mandarin.
The family also tried their best to speak Mandarin at home; however, English conversations had become more common.
"Because they go to school now, they come back speaking a lot of English."
Kids learn te reo at school
Mt Maunganui parents Tessa and Tamati Cameron are kept busy with four children under 10.
The couple, both 32, were one of the families the Herald spoke to when the Growing Up in New Zealand study produced its first report four years ago.
At the time, Mrs Cameron was pregnant with her fourth child Victor, now aged 3.
The young family were also saving for their first home - a dream that came true in 2012.
Mrs Cameron said their four-bedroom home with a two-bedroom flat was "a bit of a miracle".
"The flat was rented out to two young guys, which helped pay the mortgage."
Isaac, 5, who is part of the longitudinal study, started school this year and was thoroughly enjoying it, Mrs Cameron said.
Like his older siblings Tawhai, 9, and Evita, 7, he was learning te reo.
And unlike many of the children in the study, the Camerons were not allergic to anything, meaning meal times were relatively simple.
"Izzy had eczema," Mrs Cameron said, "but he seems to have grown out of it mostly."
Getting to grips with allergies
Hamilton 5-year-old Finn Musty is allergic to milk, egg and nuts and also suffers from asthma.
Unlike his twin brother Alex - who has no allergies and is not asthmatic - Finn has had to learn what he needs to do to stay healthy and safe.
The boys' mother, Katie, 38, said checking what is in food and using asthma medication is all part of the daily routine.
Both the twins, who have two older brothers, are part of the Growing Up in New Zealand study.
Finn, whose eldest brother Samuel also suffers from asthma, is still learning to notice problem signs around his condition, Mrs Musty said.
"If he's recovering ... I tell the teacher he's got to go to the office [for his medication] at lunch time and any other time that she feels he's coughing too much."
Samuel, 10, had reached an age where he recognised when he needed his asthma medication at school and did not need a teacher to remind him.
Finn was admitted to hospital in November after an asthma attack and stayed overnight.
"If I'm giving an inhaler more than every 15 or 20 minutes for two hours, they need more support," Mrs Musty said.
Managing Finn's food allergies had been about making him aware of what was harmful to his body, she said.
"He couldn't touch a raw egg, even hold an egg shell, but if an egg's cooked in a cake it's diluted enough and he's fine.
"But hundreds of foods have got eggs, milk and nuts in them ... and he's tolerating that, and the allergist advice we've had is leave him on it because while his body is tolerating it he's learning to cope with it."
Finn also knew to ask what was in food before eating it, she said.
Digital native at just 16 months
Four-year-old Piya Mohal started using an iPad when she was around 16 months, putting her in a select group of Kiwi kids who became digital natives as toddlers.
She is among the 15 per cent of the children in the Growing Up in New Zealand study to be using a computer system at age 2 years.
An only child in an Indian family, she uses the tablet computer for about 90 minutes a day, although her parents restrict her to no more than 40 minutes of watching television.
Piya's father, Jatender, the research data manager for the study, said he and Piya's mother, Rashmi, who runs a family business, discouraged their daughter from watching too much TV as it was light on interactive content.
On her iPad, conversely, Piya used highly interactive educational programs to learn about language, drawing, writing and especially maths.
"She's well into doing things in fractions, how tall people are, and units and measurement. That's quite good learning for her," Mr Mohal said.
He believed the educational computer programs would give Piya, who attended early childhood learning centre Kiwi Supertots, a competitive edge and help her to settle into school once she started.
Mr Mohal had been assured by an optometrist that Piya's need for spectacles arose from astigmatism and was unrelated to screen use.
He was careful not to let her over-do her digital learning, making sure she learned how to use pencil and paper as well, and books are read to her regularly.
"I understand she needs time to go to the parks and beaches," Mr Mohal said. "That's what New Zealand is all about."
Families on move regularly
Nearly a third of families in the Growing Up in New Zealand study had moved home within the previous 15 months.
The study found that 32 per cent of Auckland/Waikato subjects recruited into the research had moved at least once between the two interviews - when their children were aged 9 months and then 2 years.
In an earlier phase of the research, between the interviews during pregnancy and at 9 months old, 25 per cent moved.
The families who moved between the 9-month and 2-year interviews were more likely to be Maori than NZ European, and more likely to live in private rental housing than in their own home.
Crowding levels persistent
More than 20 per cent of infants in the study lived in moderately or severely crowded homes.
Levels of household crowding were virtually unchanged between the 9-month and 2-year interviews.
Household crowding is associated with an increased risk of illnesses such as meningococcal disease, gastroenteritis and pneumonia.
There was some movement between crowding categories.
Around 300 children and their families were living in more crowded homes at 2 years of age (compared with when they were 9 months). A similar number had moved into less-crowded conditions. Median household size increased between the two interviews, from 4 to 5.
Child-care use rises with age
The proportion of infants in childcare rose sharply as they became older.
At 9 months, 35 per cent of children were cared for regularly by someone other than their parent. At 2, that proportion rose to 56 per cent.
At 2, the children were spending on average 24 hours a week at their main type of childcare.
That was a daycare centre or kindergarten for 58.9 per cent; a grandparent or other relative for 15.7 per cent; organised home-based care programmes such as Barnardos (9.8); nanny (5.7); kohanga reo (4.4); Pacific Islands early childhood centre (2.2); and "other", including neighbours or church creches (3.3).