The existence of these places or states is supported by many dozens of Biblical passages. A person's eventual destination is determined by their salvation status at death.
Most people die as adults.
When they were newborns, they suffered from original sin. However, an infant is saved from this state at baptism. Once a person reaches the age of accountability, any future mortal sin can cause them to lose their salvation, so that they would be sent to Hell at death. However, by confessing their sin to a priest in the Sacrament of Penance , if one is genuinely committed to never repeat the sin, one's salvation is restored. A fertilized ovum, morula, zygote, embryo or unborn fetus are all regarded by the Roman Catholic church to be a full human being.