The main walkway outside the hospital was renamed Dame Shirley Bassey Way in recognition of her support for the charity set up to fund it.
The singer, who is a patron of the Noah's Ark Appeal, was given a tour before the ceremony.
She also met staff and patients at the recently opened Â£64m second phase of the hospital.
Dame Shirley said the naming of the road was an honour on a par with being made a dame.
She hugged the sign and said the last time she visited, there was no roof and she was in a hard hat.
Dame Shirley Bassey was honoured at the Children's Hospital for Wales in Cardiff on Saturday.