Pupils from Caegarw Primary School in nearby Mountain Ash, Rhondda Cynon Taf, were on a visit to the memorial garden, built on the site of the destroyed Pantglas School, on Monday morning, unaware that the prime minister would also be there.
Burnham met pupils including Ellis, 10, whose granddad travelled across the valley to Aberfan to help with the rescue effort.
“It means a lot to me and he tells me stories,” said Ellis, who described visiting the memorial garden as “emotional”.
Holly, aged 10 from Caegarw, also told the prime minister she had a personal connection with the tragedy.
“I told him about my godmother’s daughter being one of the children who passed away in the disaster,” she said.
“He said ‘wow’. It means a lot for us to be here.”
Burnham stopped to chat with local residents after visiting the garden before heading to the nearby community centre.
King Charles III, Queen Camilla and Prince William will visit the town on Wednesday to mark the anniversary, following on from the late Queen Elizabeth II who visited Aberfan eight times.
Queen Elizabeth’s reaction to the disaster in Aberfan was said to be one of the biggest regrets of her 70-year reign.
