Dr Nagel says the first three years of a child's life are critical years for the development of neural pathways. Different mechanisms of the brain are at work and these pathways are strengthened through consistent messaging.
In that same time, the brain's most primary purpose – what it's designed to do – is most evident: that's, first, to survive and, second, to learn.
That means, in effect, the predictability of the child's environment, the people they are interacting with and the messages they are receiving, are what will make the child feel safe and secure. That's looking after the survival function.
Then, the consistent setting and maintaining of boundaries and borders is what enables the development of neural pathways around self-regulation, impulse control and what's acceptable and otherwise. Therein lies the learning.
Australian parents have some room for improvement when it comes to setting boundaries, according to results from the recent First Five Years' Snapshot of Australian Families survery which found 40 per cent of parents would rarely or never give in to their child’s demands to avoid a fight or to keep them happy., while 12 per cent said they often or always gave in.
Dr Nagel uses the example of having a snack before dinner time.
"If my son comes up to me and asks for a snack before dinner, and I say no, he is likely to try everything from eye-rolling to being curled up in the foetal position on the floor crying about how hungry he is.
"In the early years, there is actually something in that because if the child feels hungry, and they are not allowed to have a cookie or a snack, then their brain will go into survival mode and that then brings on the emotional response.
"But if you consistently stick to the same stance and have the same answer every time, the neural pathway will develop that a cookie isn't going to be allowed before dinner."
Dr Nagel says that also helps mitigate against a survival response when being told they cannot have the snack.
The problem, however starts when you're not consistent.
"If you say no, and then buckle – which, let's face it, is easy to do when they look heart broken or are persistent – and say yes, that is nurturing a whole different neural pathway. You're not setting the boundaries and they are not being taught self-regulation.
"The same thing applies whatever the situation for which you are trying to establish rules, borders or boundaries."
Not only is a lack of boundaries hard work in the longer term for parents, but it can set kids up to fall short of their own potential as well.
"There is now a lot of research and evidence that shows kids with good impulse control will typically be healthier, have better grades and be overall less susceptible to anxiety and stress,” Dr Nagel says.
"Boundaries are not just important for parents.
"Think about it: The better we are, at controlling our emotional impulses, the better we will do when we set our mind to it."
And the key is setting these boundaries and having this predictability and behaviour in place early.
"As children get older it becomes more difficult to do.
"Going off to child care or kindy and school means children will be faced with a whole new set of rules and boundaries and even the approach different teachers will take will fluctuate.
"That's why establishing these as early as possible will make it easier for your child to adapt to new rules and situations and understand that they are necessary."
As kids grow, Dr Nagel says, it just gets harder if the ground work isn't done early on.
Remaining calm, keeping consistency and creating that predictable safe environment is the best thing a parent can give their child.
"The fact is, whatever you do in the early stages is setting your child up for the rest of their lives.
"And if you have trouble saying no to a four-year-old, then that difficulty is only going to grow exponentially when they're 14."