The visit was especially special as the mother-of-three was made a patron of the children’s hospital.
Helping to welcome them was 6-year-old Tiana Yales, who is being treated for sickle cell anaemia and was chosen to present a bouquet to the royal mom.
After giving Kate the flowers and shaking her hand, Tiana smiled as she did a quick (and bouncy!) curtsy.
While visiting the clinic, which is set to mark its 150th birthday next year, the royal parents spoke with staff and parents and met children as they took part in Christmas-themed fun.
During an arts and crafts session , Prince William and Kate helped children make some beaded bracelets, something it seems Princess Charlotte would have loved according to the royal mum.
"Charlotte would love making these."
William laughed crafty shortcomings as he helped to make a welcome sign for the charity's upcoming Christmas party.
Cutting out the letter E, William said: "My son knows I'm useless at this. Catherine is the artsy one."