The Duchess of Cambridge has been lying low since her third pregnancy was announced earlier this month by Kensington Palace.
The 35-year-old was forced to take a break from public duties due to a health condition called hyperemesis gravidarum, which she suffered throughout her two previous pregnancies.
Now, Catherine has launched the 'You're never too young to talk mental health' campaign by the Anna Freud National Centre for Children and Families, of which she is a patron.
As part of the initiative, Catherine appears in a video teaching children about their mental health and strategies they can use to understand and manage it.
“Mental health is how we feel and think,” the mother of two explains in her introduction, which was recorded in January.
“Things that can’t really be seen but affect us every day and talking about them can feel difficult.”
The mother of Prince George, 4, and Princess Charlotte, 2, also wrote an introduction to a leaflet designed to help parents and carers open up conversations about mental health with children.
"As parents, we all want our children to have the best possible start in life," she wrote.
"Encouraging children to understand and be open about their feelings can give them the skills to cope with the ups and downs that life will throw at them as they grow up.
"It's important that our children understand that emotions are normal and that they have the confidence to ask for help if they are struggling."
This isn’t the first time Catherine has been an advocate for mental health awareness.
Last year, she joined Prince William and Prince Harry in spearheading Heads Together, a campaign aiming to address the stigma surrounding mental health.
She also released a video for Children's Mental Health Week in 2016, saying she and William "feel that every child deserves to be supported through difficult times in their lives".