The teenagers are understood to have been on the run from a foster home in Varberg in southern Sweden when the killing took place on Tuesday night.
“It's highly unusual that such young people are suspected of such a serious crime as murder,” police investigator Cecilia Bergsten said in a statement on Wednesday.
“We need to methodically continue collecting clues from the crime scene to get a picture of the events,” she added.
The two boys were on Thursday understood to be in the care of Swedish Social Services.
Bergsten's police statement added that the boys had been “interrogated” but noted that no further details would be disclosed about their alleged involvement in the crime.
It is understood that one of the pensioner's family members raised the alarm on Tuesday after fearing a burglary at the farm, where police later found the man dead.
Officers arrested the boys after witness statements and objects believed to belong to one of the teenagers linked them to the scene, Sweden's TT news agency reported on Wednesday.
According to the online edition of Gothenburg tabloid GT, the boys are not thought to be brothers, although it remains unclear if they are otherwise related.
In Sweden, children under the age of 15 cannot be charged with a crime or go on trial. Instead, they are placed in the care of social welfare authorities.
Police are not allowed to hold children under 15 in custody either, but can interrogate them as part of an investigation.