CILACAP, Indonesia (AFP) - Led by the hand through a scrum of reporters to an Indonesian prison island, the six-year-old Filipino looked confused and frightened as he made one of his final visits to his mother before her execution.

During the visit to Nusakambangan Island, Filipina maid Mary Jane Veloso gently explained to six-year-old Mark Darren and her second son, 12-year-old Mark Danielle, that she would not be coming home.

"She tried to explain again," Veloso's elder sister Marites Veloso-Laurente told AFP during an interview in Cilacap, the port town that is the gateway to the island.

"If Mumma does not go home, just think Mumma is in heaven."

As the clock ticks down on the execution by firing squad of eight foreign drug convicts, heartbroken relatives who have fought for years to save their loved ones are rushing to say final farewells.

The convicts, who also include nationals from Australia, Brazil and Nigeria, all recently lost clemency appeals to President Joko Widodo. They could be put to death as soon as Tuesday after they received official notification of their executions at the weekend.

Veloso's two sons travelled with their family - some of whom had never flown - from an impoverished community north of Manila to hear a message almost impossible for them to take in.

Veloso, 30, was convicted of trafficking heroin into Indonesia in 2009, but says her only crime was to fall victim to international drug gangs who are now threatening to kill her family if they speak out.

Her case has drawn huge attention in the Philippines, with supporters calling for clemency at regular rallies in Manila. Even world boxing superstar Manny Pacquiao pleaded Monday for her life to spared, taking time out from preparations for his fight against Floyd Mayweather.

- Clinging to hope -

Two other high-profile inmates are the Australians, Myuran Sukumaran and Andrew Chan, ringleaders of the so-called "Bali Nine" heroin-trafficking gang. Numerous family members and embassy officials have been rushing to visit them since notice of execution was given.

On Monday one of the lawyers, Todung Mulya Lubis, returned from the prison where they are being held carrying a self-portrait by Sukumaran, an accomplished artist, entitled "The second last day".

Veloso's family are clinging to hope her execution will be delayed so they can pursue an application for a second judicial review of her case - but with formal notice now served, such efforts are looking increasingly futile.

While the execution of drug traffickers has broad support in Indonesia, there has been some sympathy for Veloso, as many Indonesian domestic workers have also been executed while working abroad.

As her family wept and prepared to cross to Nusakambangan for what could be the last time on Monday, supporters turned out waving "Save Mary Jane" banners and urging them to keep their spirits up.

But the show of support could do little for Veloso's mother Celia. Her calls for Widodo to spare her youngest child are growing increasingly desperate.

"She says 'My daughter is innocent... it's not easy to lose someone like her'," Father Harold Toledano, a Filipino priest assisting the family, told AFP.

Veloso is hoping for an 11th hour miracle and Laurente is appealing directly to Widodo to spare her sister.

"I would like to convey to you it's only God who has the right to take away the life of anyone," she said in her message to the president.

Laurente is particularly fearful for Veloso's young sons, who played happily with toy cars at their hotel, oblivious to the family's mounting desperation and officials swirling around them.

But she knows Mark Danielle will always keep a watchful eye over his younger sibling, recounting a pledge he had made to his mother in recent days.

"He promised his mother that he will take care of his younger brother and they will study hard," she said.