George played a sheep in his nativity play, William tells schoolchildren

Asking the children about their plans for Christmas, William said: “I went to my boy’s nativity play. It was funny.”

He added: “He was a sheep.”

The couple attended a “stepping out” session – a focus group for children to give feedback on new programmes to children’s TV producers and editorial staff.

Kate, who is expecting their third child, wore a long-sleeved red dress.

The couple met BBC director general Tony Hall, chief adviser of BBC Sport Neil Land and the director of BBC Children’s Alice Webb as they arrived at the offices.

They then joined children from Friars Primary School in Salford who had watched a film created by 14-year-old Josh Gale for Newsround about developing obsessive compulsive disorder.

The Duchess of Cambridge meets well-wishers in Salford (Danny Lawson/PA)

In a question and answer session with the children, Josh explained he had told his father about his mental health problems.

He said: “It was metaphorically and physically like a weight off my shoulders.

“I was wanting to tell someone but I thought no-one would understand.”

The Duchess of Cambridge greets children – as well as some famous faces (Danny Lawson/PA)

William told the children: “You’re much better than the adults at questions. Very good questions.”

The couple joined children for group discussions where they both encouraged the youngsters to talk about mental health.

Kate said: “People are so worried about what they say, they aren’t saying anything at all, and what we’ve found from speaking to people is it’s so good to have conversations.”

William said: “Mental health used to be this scary word that people didn’t like talking about and it’s slowly getting better now.”

The Duke and Duchess were greeted by children’s characters including Danger Mouse, Peppa Pig, Elmo from Sesame Street and Postman Pat as they arrived at the Children’s Global Media Summit in the Manchester Central Convention Complex.

A warm welcome for the duchess (Danny Lawson/PA)

The couple then met delegates from the conference, which is on the future of children’s media.

Jeffrey Dunn, chief executive of Sesame Workshop, said William told him he had seen Elmo outside.

“He was remarking on how exciting it was,” he said.

Alex Okosi, executive vice president and managing director of Viacom Africa, said he spoke to the Duke about the work the company was doing to help young people without access to education.

He said: “He understood the importance of education and trying to bridge that gap between those with unlimited access and those who will never get it.”

He added: “He was a really cool guy.”