The incident happened Sunday in the home of the victims, who were identified as a brother and sister, both less than 10 years of age, the Boston Globe reported.
"Investigation to this point indicates that the children were found by family members shortly before 8 p.m. enclosed together in a hope chest fashioned with a lid that could only be released from the outside, and not opened from within," Norfolk District Attorney Michael Morrissey's office said in a statement Monday.
Other family members were home at the time of the incident, but "the hope chest was in relatively close proximity to a television that was apparently on with a substantial volume at the time," the statement said.
The incident is currently being considered an accident, prosecutors said.
Millions of Getty images now available for free via embed tool
Boston schools pull out free condoms over wrapping complaints