The family held a double burial on Saturday for the siblings, who first went to Apia's hospital for a measles check eight days ago, the Samoa Observer reports.
The one-year-old has a twin, who is now the sole remaining child of a couple from Lauli'i - a coastal village outside Apia on the island of Upolo.
Last week, the Health Ministry's Public Health specialist said the two-year-old boy's clinical file was being reviewed to assess his cause of death but it was thought to be related to the measles virus.
The Ministry of Health has been approached for confirmation of this latest death.
The number of total suspected measles cases in Samoa with the current outbreak is 513, with results still pending from an Australian laboratory regarding the recent deaths of two infants and an adult male, who showed clinical signs of the disease.
Vaccination and quarantining as well as infection control measures at the hospital are all being coordinated by the ministry which is working closely with the World Health Organisation, UNICEF, the New Zealand government and an Australian medical laboratory to contain the epidemic.
A measles epidemic was declared in Samoa last month.
