Kate, 32, braved a bitterly cold frosty morning, wearing a red Katherine Hooker dress, to attend the launch at the Norfolk Showground in Norwich.
She met families, volunteers and supporters from the East Anglia Children's Hospices (EACH) charity of which she has been a patron since 2012.
The charity currently has a Norfolk hospice in the village of Quidenham but it is old and outdated with limited resources.
The ambitious appeal hopes to raise enough money to build and equip a new hospice, The Nook, in Framingham Earl, Norfolk, to help the county's sick children.