Earl Spencer, Diana's brother, also attended with his children. He said he was not upset by the Royal Family's decision not to attend.

Domenica Lawson officially opened the playground

"People came who wanted to come and it was a happy occasion. One of my sisters did not want to come because she thought she would be overcome by the emotion of it all - it's very difficult," he said.

They joined Diana's close friend Rosa Monckton and her five-year-old daughter Domenica Lawson, the late princess's godchild, to open the playground in Kensington Gardens.

Domenica, who suffers from Down's Syndrome, untied a ribbon to declare it open.

With the help of her mother, she said: "I open this garden for godmother Diana."

No 'snub'

Ms Monckton said Diana had taken her duties as godmother very seriously and had attended Domenica's early therapy sessions.

"She fought for her as she fought for all children with disabilities. I know how proud she would have been that it is her god-daughter who is opening the memorial garden today," she said.

A member of the Diana, Princess of Wales Memorial Committee described the decision of the Royal Family not to attend as "sad".

The princes declined the invitation to attend

But Buckingham Palace said their absence was not a snub to Diana's memory.

St James's Palace said the Prince of Wales will be in Dorchester attending a number of "public and private engagements".

"He has long-standing commitments and he is always careful not to let people down."

Prince William and Prince Harry were asked if they wanted to attend the opening but declined, a spokeswoman said.

She added: "That was a very private and personal decision they made for themselves."

The Queen would be in Scotland from Thursday for Royal Week, the Palace said.

Totem poles

The Diana, Princess of Wales, Memorial Walk is marked by 89 plaques charting the seven-mile route through Kensington Gardens, Hyde Park, Green Park and St James's Park.

The �1.3m walk features fountains and memorials as well as improved landscaping and restored ornamental gates.

The garden is based on the story Peter Pan

The �1.7m playground, close to Diana's former home at Kensington Palace, is based on a Peter Pan theme because J.M. Barrie, creator of the classic children's story, funded a playground on the site in 1906.

It has six play areas, including a sculpted water feature called the Mermaid's Fountain, the Wigwam Camp with totem poles and tepees, and a Movement and Musical Garden.

Mr Brown said the playground was for the people Diana cared about most - children, including children with disabilities.

He said: "We decided that there should not only be the Diana, Princess of Wales nursing teams, caring for sick children across the country, and a special memorial award for young people, to encourage community service and excellence, but also a walkway and specially-designed memorial playground."

The development followed more than 10,000 suggestions from members of the public about the way Diana's life should be marked.