Human blood has reportedly been found on a toy car and sandal believed to have belonged to toddler Ben Needham, who disappeared on Kos 26 years ago.
Kerry Needham said the discovery is evidence of a cover-up in the disappearance of her son, who was staying at his grandparents' farmhouse on the Greek island.
She fears the 21-month-old was killed and his body moved before British police began searching the site last year.
South Yorkshire Police formally ended a search on the Greek island last October, saying they believe Ben died as a result of an accident involving a digger on July 24 1991.
Despite extensive searches of two sites his body was not found.
Ms Needham, 43, begged for anyone with information about what happened to her little boy to come forward.
"This confirms everything the police have suspected. It makes it all a little too real. We believe what they believe," she told the Daily Mirror.
She added: "It shows more of a conspiracy because they didn't find Ben's body.
"That proves it to me without doubt they obviously moved him and buried him and for whatever reason dug him up.
"There's no other explanation. It's all been a massive cover-up."
The sandal was reportedly found in 2012 at the site where Konstantinos "Dino" Barkas was operating a digger, while the car was discovered last year at another spot.
Mr Barkas is believed to have died from stomach cancer in 2015.
The sandal and car will now be tested for Ben's DNA.
Professor Lorna Dawson, of the James Hutton institute in Aberdeen, has been working with South Yorkshire Police.
She told the Daily Mirror a specialist police dog used in the hunt for bodies had reacted to the sandal and biologists were trying to extract DNA from both items to compare with Ben's profile.