Scientists say it can also determine whether we succeed in life and increases the chances of who can become either prime ministers or prisoners.
"The primary influences that will determine your success in life are set in those first four years - the first nine months before your birth and the three years after you're born," says Sir Peter Gluckman.
He and his colleagues at Koi Tu: The Centre for Informed Futures say if executive functions - such as planning, thinking, memory, and emotional regulation - don't develop properly, there can be lifelong consequences. It can determine if you fail at school, have poor mental health, get involved in crime, and ultimately could be passed on to the next generation.
The scientists say there's research that shows by two years of age, they can somewhat predict what can happen to people over the rest of their lives.
Good executive functions are tied to positive environments, including a calm and happy pregnancy, positive and active interactions with parents and caregivers, less screen time, and more time hitting the books.
All of these things are especially tough for parents and caregivers struggling in poverty, and Sir Peter is calling for better policy to address inequities.
"It's not just about economic support, it's about other forms of emotional and social support as well," he says.
To ensure all tamariki have the best start so they can go on to lead better lives.