"The Nelson Mandela Children's Hospital is a monument of the love, care for children by Madiba himself.
"The hospital is a monument of excellence, it is also a monument that reminds South Africa and Africa that excellence is possible.
"When we say 'Children First, we really mean it. Children deserve the very best we can provide [and] children are to have, in this hospital, the very best we can provide," Machel said.
She was speaking at the hospital's launch in Parktown, north of Johannesburg, on Friday.
The state-of-the-art hospital was only one of four specialised children's hospitals on the continent, and only one of two in the country.
Construction on the R1 billion healthcare facility began in April 2014 and consists of 200 beds. It will be a referral based hospital, however, it has pledged not to turn away any child in need of care.
The hospital will also be a centre for specialised pediatric care.
"From now on, there are no excuses to give second and third class treatment to kids," Machel said.
She said, while her husband was alive, many people had made promises to him, saying they would make sure his legacy lived on, even after he had died. The hospital was proof of that, she said. She also said that the fact that the hospital had indeed materialised, meant that he had kept his promise to the children.
"A promise to a child is to be fulfilled. Never promise to a child what you are not sure you are going to deliver."
'We promise you we will try our best'
The hospital was an expression of the saying, "every child counts, every child matters", she added.
It was also proof of successful cross-border collaboration because "people around the world contributed to make it happen".
The hospital would provide services to children from all countries in the Southern African Development Community.
Mandela had left South Africans with a lesson; that there be no compromise when it came to caring for children, and this was what everyone would work to achieve, Machel said.
"That is the lesson that you left with us papa, and we are going to try [to do that] in caring for every child of the world."
Machel also urged South Africans to do their part in making their country a society which was known for its stance on social justice.
"No children should continue to die unnecessarily in our hospitals. No child should live I fear of being brutalised by violence against children.