Kate is patron of Evelina London and was greeted by the hospital’s chief executive, Gubby Ayida.
The princess will open the hospital’s day surgery unit and meet young patients and their families to hear about the positive impact it is having on their lives.
Evelina London cares for around 104,000 children and young people each year across its dedicated children’s services, in hospital and in the community.
The new facility aims to transform care for those who need surgery, by providing everything in one place, enabling Evelina to treat an extra 2,300 children a year in addition to 11,000 already receiving surgery.
Kate will see the two new operating theatres and hear how families benefit from a one-day service, with pre-surgery checks, the operation and recovery all taking place in one purpose-built unit.
Ms Ayida said: “We put children, young people and families at the heart of everything we do, and you especially feel that when coming into our new unit.
“It was lovely to have this recognised with the Princess of Wales today, who values the importance of having a supported and nurturing environment for children through her work with The Royal Foundation Centre for Early Childhood.”