The Duke and Duchess of Cambridge will attend an assembly with primary school pupils to mark the start of Children's Mental Health Week today.
Kate, who is patron of charity Place2Be which organised the "Big Assembly", will be joined by William for the visit to Mitchell Brook Primary School in north west London.
They will present a "Kindness Cup" to the child who has "has shown exceptional kindness in their school community and beyond" and meet staff and pupils.
The children's mental health charity is part of Heads Together - an umbrella campaign spearheaded by the Duke and Duchess and Prince Harry.
It aims to change the national conversation on mental well-being to a positive one and is the charity of the year for the 2017 London Marathon.
On Sunday, William and Kate, accompanied by Harry, joined runners competing in the London Marathon for Heads Together for a relay race at the Queen Elizabeth Olympic Park in east London.
On Monday evening, the couple will attend a Guild of Health Writers conference focusing on mental health, which is being supported by the Heads Together campaign.
The Anxiety Epidemic conference will have a number of guest speakers including Paul Farmer, chief executive of Mind, which is one of the eight Heads Together charity partners.
William and Kate will meet members of the Guild of Health writers and hear from a Heads Together runner, and the Duke will give a short speech.
The engagements are on a landmark day for the royal family, as the Queen becomes the first British monarch to reach their Sapphire Jubilee - marking her 65-year-long reign.
There are no grand festivities planned to mark the head of state's milestone and the Queen is not due to be out and about on official engagements.