Who do we mean by 'children'?
Children (tamariki) in New Zealand are legally people aged under 18 years [1,2]. However, health statistics often classify children aged 0 to 14 years, as many environmental risks change as adolescence becomes young adulthood. Some legislation also uses this definition and differentiates between children and young people . Early childhood is the period variably defined from conception to ages 2–4 years.
The environmental burden of disease among young children is high
Globally, a quarter of all deaths and a quarter of all years of healthy life lost (disability-adjusted life years, DALYs) in children under five years are caused by modifiable environmental factors .
The main diseases contributing to this environmental burden of disease in young children include:
- respiratory infections
- diarrhoeal diseases
- neonatal conditions (such as premature birth)
- unintentional injuries.
Children's exposure to the environment differs from adults' exposure
Children are not small adults.
- Children eat more food, drink more fluids and breath more air per kilogram of body weight, and have a larger skin surface in proportion to their body size, than adults. This means their exposure to (potentially) harm-causing agents or substances is greater for their size than in adults.
- Children absorb more of some substances (eg lead) from their gut.
- Children's behaviour, such as putting hands and objects in their mouth, as well as their play and exploratory activities, influence their exposure.
- Children may be more susceptible to some exposures because their organs (particularly their brain) and bodily systems (such as their immune system) are still developing.
- Depending on their age, children are less able to avoid hazards. 
Environmental exposures can affect the growth and development of a child from early intrauterine life through to adolescence, as well as impact their health later in adulthood.
Many factors influence children's environmental health outcomes
Parent/family (whānau) characteristics, the home and wider social and physical environment all influence a child's health and life course outcomes. These factors often interact. Some children are at increased risk due to where and how they live.
New Zealand evidence shows multiple exposures at the same time and over time to risk factors of vulnerability (eg maternal smoking, household crowding, socioeconomic deprivation) in early childhood increase the likelihood of poor health outcomes [6,7].
Early childhood is the most important period for child development
Factors influencing children's environmental health can vary markedly at different developmental stages. The foundations for physical and mental health and well-being, which affect our capacity to adapt, learn and succeed in life, are laid in early childhood. Environmental exposures during this period have greater potential for lifelong impacts, and early intervention is more likely to be effective.
Environmental exposures in early life may increase the risk of chronic diseases such as heart disease and diabetes in adulthood.
Environmental exposures at different stages of child development may lead to different health effects during a person's life and in their children.
Environmental exposures are largely preventable
While some factors that influence health cannot be changed (such as a child's genetic make-up), we can do something about their environment.
Reducing adverse environmental exposures, such as reducing pollution, improving water quality, safely disposing of hazardous waste, and making home and neighbourhoods safer, can prevent poor health.
1. New Zealand Government. Care of Children Act 2004. URL: www.legislation.govt.nz
2. New Zealand Government. Vulnerable Children Act 2014. URL: www.legislation.govt.nz
3. New Zealand Government. Oranga Tamariki Act 1989. Children's and Young People's Well-being Act 1989. URL: www.legislation.govt.nz
4. Prüss-Üstün A, Wolf J, Corvalán C, Bos R, et al. (2016). Preventing disease through healthy environments: a global assessment of the burden of disease from environmental risks. Geneva: World Health Organization. URL: http://apps.who.int/iris/ bitstream/10665/204585/1/9789241565196_eng.pdf?ua=1 (accessed 3 July 2018)
5. World Health Organization. (2017). Inheriting a sustainable world? Atlas on children's health and the environment. Geneva: World Health Organization.
6. Morton SMB, Atatoa Carr PE, Grant CC, Berry SD, et al. (2014). Growing Up in New Zealand: A longitudinal study of New Zealand children and their families. Vulnerability Report 1: Exploring the definition of vulnerability for children in their first 1000 days. Auckland: Growing Up in New Zealand.
7. Morton SMB, Atatoa Carr PE, Grant CC, Berry SD, et al. (2015). Growing Up in New Zealand: A longitudinal study of New Zealand children and their families. Vulnerability Report 2: Transitions in exposure to vulnerability in the first 1000 days of life. Auckland: Growing Up in New Zealand.