As reported in Latin American Antiquity:
"At Salango, a ritual complex on the central coast of Ecuador, excavations revealed two burial mounds dated to approximately 100 BC. Among the 11 identified burials, two infants were interred with “helmets” made from the cranial vaults of other juveniles. The additional crania were placed around the heads of the primary burials, likely at the time of burial."More details at Live Science:
The helmets were placed tightly over the infants' heads, the archaeologists found. It's likely that the older children's skulls still had flesh on them when they were turned into helmets, because without flesh, the helmets likely would not have held together, the archaeologists noted.