Kate Middleton and Prince William were welcomed with kisses and high-fives as they learned about the Swedish approach to good mental health.
William and Kate were greeted affectionately by their Swedish hosts Crown Princess Victoria and Prince Daniel on the second day of their Nordic tour when they arrived at a leading medical research centre.
Victoria and Daniel, who were guests at the Cambridges' 2011 wedding and are getting to know their distant UK relatives, showed their growing bond with the British royals with the warmth of their welcome.
Kisses on both cheeks were exchanged between the royal women and Daniel and William shook hands outside the Karolinska Institute in a snowy Stockholm, where the foursome met leading scientific researchers to discuss groundbreaking academic work in managing mental health challenges.
The duchess, who is around six months pregnant and clearly showing her baby bump, wore a Catherine Walker coat, a dress by Alexander McQueen and Swedish earrings by In2Design.
Later at the Matteusskolan, a combined primary and comprehensive in the city centre, the duke, duchess and the Swedish royals went on a walkabout meeting dozens of children waiting to greet them outside.
William and Kate high-fived a number of children from the school bending down to speak to the youngsters.
The duke repeatedly told them "you've got cold hands" and complimented the youngsters on the Swedish flags they were waving.
One teenager, more in hope than expectation, quizzed the duchess about her taste in rap music.
"I asked her if she knew J Hus," said Lucas Tinseau, 15, "She said 'I will look out for him'."
At the Karolinska Institute the Cambridges joined a discussion on the correlation between mental health in young people and physical exercise.
The duke and duchess were at the world-famous medical university to learn more about its research into the impact of physical activity on people's mental well-being.
The Crown Princess has spoken openly about her own battle with an eating disorder as a young woman while her husband, a former fitness trainer who opened a chain of exclusive gyms, is interested in the subject and started his own programme to promote physical well-being in the young.
William and Kate have made campaigning on mental health issues one of the central themes of their public working lives.
Their Heads Together mental health campaign saw a series of events staged last year to encourage Britons to talk about their psychological problems or provide a sympathetic ear for others.
The royal foursome were briefed by senior staff including Dr Ulrika Berg who outlined some of their research.
Dr Berg said: "I am a paediatrician and meet a lot of children with mental problems. It is absolutely important that we use physical activity as a tool for prevention and also for treatment for... mental diseases such as depression."
"I think people think 'oh, it is good for children to move'. But it has really been shown, in research, that there are important effects, for example in depression when we know that self-esteem increases."
Later at the school the four royals watched pupils take part in a role-playing exercise exploring family problems.
They also spent time privately talking to young people about the emotional issues they face.
The royal party were marking the 10th anniversary of the Youth Aware Mental Health (YAM) programme, which encourages young people aged between 14 and 16 to help each other battle a wide range of emotional and mental health problems.
In the school hall, they heard one teenage student, Hugo Steg, make a speech in English about his experiences doing the course and supporting his friends.
William told an audience of teachers, students and mental health practitioners: "Catherine and I and Victoria and Daniel care deeply about mental health. It's all about early intervention. Sometimes a conversation is enough."
Later William and Kate travelled to the Haga Palace, Crown Princess Victoria and Prince Daniel's official residence, for a private tea with the couple.
Victoria is the modern, approachable and down-to-earth face of the Swedish monarchy who married her personal trainer Daniel Westling after a long period as a couple like William and Kate.
They now have two children, five-year-old Princess Estelle and one-year-old Prince Oscar, with Daniel a house husband.
Pictures released following the private tea showed the Cambridges meeting the Swedish royal couple's children with their proud parents.