We’re walking through an "ivory tower", a few doors away from where the father of psychoanalysis, Sigmund Freud, spent his final years.
Forget the caricature Hollywood psychiatrist in a pristine white lab coat, Dr Bevington couldn't be more approachable in his jeans and an open-necked shirt as he leads me past a colourful coat stand for children and into a room filled with Lego.
"Thirty to 40 years ago we thought we could put kids into a childhood machine and they would pop out and we would deal with the problems later," says Dr Bevington, the centre’s medical director or, as he puts it, "the shrink".
Downstairs at the Anna Freud Centre, which is at the forefront of research into child mental health, a roomful of health professionals are being trained to help young people deal with trauma.
In the waiting area, a couple catch my eye and flash a nervous smile. The centre also offers assessments of families and children for court cases.
"Very early in my career, I remember talking to an old acquaintance about mental health. The response was, 'Wouldn't it be better if these people were just put down?' You can't get more offensive than that," says Dr Bevington, laughing in disbelief.
It's a theme which runs strong through my tour, part of The Huffington Post UK's Young Minds Matter series, guest edited by The Duchess of Cambridge.
Mental health experts have always had an uphill battle when it comes to asserting the importance of their work and research involving children has been neglected more than just about anything else.
However, Dr Bevington is an optimist and he means to be encouraging when he says: "Mental health today is where general medicine was 100 years ago."
Although this might not sound like progress, the more we talk, the more it becomes clear how far care for children has come.
"Nearly 50 to 60 years ago babies weren't given anaesthetic during operations because it was thought they couldn’t feel pain," he says, nodding (and smiling) in acknowledgement of my silent shock.
The assumption was that the adolescent brain was the same as an adult brain, except it needed more training.
"The brain is the organ of the mind. We're just beginning to get to the point where we can really explore it on multiple levels," he adds. "Broadly speaking, we have a theoretical understanding."
I spot a camera as we continue our walk through the building. Dr Bevington tells me it is used to capture footage that therapists can later analyse.
Research is very much the heart and soul of the Anna Freud Centre.
But work in the field is being held back because children with mental health issues don't have a voice, Dr Bevington believes.
While copious amounts of money pours into tackling higher-profile problems, such as cancer, research on mental health in children is severely underfunded.
Most cancer sufferers are much older when they get ill and know how to articulate their stories, says Dr Bevington.
"Mental health has always been massively stigmatised," he adds. "People are terribly alarmed at the idea and want to make it completely different from our ordinary lives. The reality is that one in ten children under the age of 16 have a diagnosable condition."
Nonetheless, research into children's mental health is focusing on prevention rather than cure.
Early intervention is crucial. "We're essentially growing the brain that will help the children navigate the rest of their lives," says Dr Bevington.
"If you intervene early there is a real genuine hope to alter the trajectory of a young person's life in a way that, if you pick them up at 25 or 26, they're largely set in what they've got."
Dr Bevington's eyes light up as he talks about his patients. "The young people I work with - they're inspiring. They manage life situations that most of us would be crushed by."
He is wonderfully apt at avoiding an 'us and them' mentality when talking about young people with mental health issues.
"We know that all of us are vulnerable," he says. "Most of us had points in our lives where we have had crisis and know that we weren’t thinking as clearly as we should have."
To explain how much progress is being made in the field, Dr Bevington likens the approaches used by mental health professionals to looking at the same problem through different lenses.
"In the last five to ten years, we have realised that a lot of these models are quite different in the way they make sense of the problems," he explains.
The cognitive behavioural therapy (CBT) model makes sense of human behaviour by diving into thoughts, feelings and behaviours.
"If a child starts to have fearful thoughts this could make them believe the world is a dangerous place and, therefore, they choose to stay in their bedroom," says Dr Bevington.
"A CBT therapist would approach this by helping them test the truth of some of those thoughts."
A systemic therapist, however, believes this behaviour is part of a wider problem, such as alcoholic parents, which then demands a solution for the entire family and not just the child.
Other therapists use a model which looks at a child's deep-seated fears.
But it's the models themselves that have often slowed progress in the field, Dr Bevington believes.
"Twenty years ago we were invited to have more interest and expertise in the model than in the patient," he explains.
This led to a "tribal battle" between the models. Now, the emphasis is on a more collaborative approach, moving beyond these competing ideas.
Dr Bevington divides his time between NHS work and the Anna Freud Centre and appears to have an endless supply of patience and understanding.
He prefers a mentalisation-based approach to treatment. It is "a very conscious attempt to draw on all three models and bring them together with brain science", he says.
"It makes sense of your behaviour by helicoptering my imagination into your shoes."
Seeking a greater understanding of the approach, I call Dr Bevington the next evening. "Well, let's see," he says. "Why is Nitya calling me on a Saturday evening…well, she must have a deadline and she must need to fix something."
He begins to "mentalise" me and, though I'm grateful for a little psychotherapy, I start to get a sense of what his patients must feel when they visit him.
"Before 1996, 'mentalisation' was never a searched term in Google," he adds. "Now there are hundreds of thousands of searches.
"The research is leading us to a brand that looks at the common factors that make these treatments effective."
Critically, it is now more about the patient than the type of psychotherapy.
Says Dr Bevington: "Whether or not you explain the problems by the CBT or systemic model is less important than a practitioner having a map to make sense of the problem and, more importantly, the therapist needing to create more trust between them, the child and family."
EMDR (eye movement desensitisation and reprocessing) is among the emerging new therapies which lend themselves to helping primary school children.
It helps them overcome "vivid, unwanted, repeated recollections of traumatic events," simply using eye movements.
"Why it works wonderfully well is that it doesn't require a complicated level of understanding or language," according to child therapist Nick Adams.
"You're moving your finger in front of the child’s eyes for 15 seconds and then you stop and ask the child to draw a picture of what is in their mind right now after the moment."
With time, the negative imagery associated with a particular memory, decreases.
Dr Bevington refers to these highly specialised areas of psychiatry as "magic bullets" – part of the solution but not the entire answer.
"Health professionals like me need to get more confident in how to spot key warning signs," he says.
"You have to have more of a democratisation of mental health care rather than thinking 'it's a bit spooky, it's a bit frightening' and 'maybe the shrinks are madder than anyone else'. We've got to move beyond that."
One of the bigger disappointments in addressing mental health in children has been the pharmaceutical industry’s offerings.
"There are no game-changing new medicines available," Dr Bevington says, "partly because the pharmaceutical industry is not interested in developing drugs for children with mental health problems, because it's difficult to pay for trials for children."
According to Dr Bevington, therapists are wary of using medications for fear the mental health condition might change.
"I'm very pragmatic," he adds. "I prescribe medicine, when the risk of not prescribing is greater than the risk of prescribing."
While some of the answers in solving this crisis may lie in science’s magic bullets, Dr Bevington has a bigger dream for how we address the problem.
"I would like to see mental health stigma addressed with a similar level of robustness and enthusiasm that has been applied to racism and sexism at the government, social and cultural level," he says.
"Just creating an environment where you can talk about these things – that is magic."
Young Minds Matter is a new series designed to lead the conversation with children about mental and emotional health, so youngsters feel loved, valued and understood. Launched with Her Royal Highness, The Duchess of Cambridge, as guest editor, we will discuss problems, causes and most importantly solutions to the stigma surrounding the UK’s mental health crisis among children. To blog on the site as part of Young Minds Matter email firstname.lastname@example.org