Asking for legal advice here, but it’s not practical, just theoretical, and therefor I don’t need answers fast.
Inheritance is left to the children of X divided equally. X has 2 born children and one fetus. Does the fetus get anything? If so when?
IANAL and I don’t play one on TV.
It will depend upon the will and the respective state law governing the will.
At common law, a child en ventre sa mere, as they say, will indeed inherit, provided it is born alive and survives for at least a reasonable period (generally taken to mean about month).
The common law rule may, of course, be modified or overridden by legislation in any jurisdiction, but in most jurisdictions that I know of the common law rule, or a statutory version of it, is still in force.
This has implications that carry over into other areas of law. For example, if somebody dies and as a result payments are due under an insurance policy, or under workers’ compensation legislation or the like, to their dependants, a posthumously-born child can typically claim as a dependant of the deceased.