Biomedical science has made some incredible advances over the years and we can only expect that trend to continue and for science to yield ever more secrets about and tools over the human body. The law, however, has not made such advances – you'll still find wills written as they were by 18th century scriveners and sprinkled with language like "party of the first part" and "witnesseth" – but then legal planning might just be forced to evolve. For your consideration: now there is such a thing as posthumous birth and post-mortem parenthood, as pointed out in this recent article as elsewhere.
Roughly half a million cryopreserved embryos and untold amounts of genetic material (sperm and ovum donations) line medical facility coolers around the country, and it's not a novelty. An increasing number of couples have made plans to preserve the possibility of a child, either because they were having fertility issues; the financial situation imposed caution while the biological clock imposed haste, or precisely out of fear that one would pass away before there was an opportunity. It also means that an increasing number of children are being produced to parents who are no longer living, and there remains the ever-increasing possibility for grandchildren of the same nature. How do parents, grandparents, and estate planners at any juncture understand the ramifications?
Frankly it will require a moment to think about the possibility and to confer with your adult children to find out if it is a possibility that you might have grandchildren who were born after their parent passed away. In many ways this is a dilemma faced by a number of grandparents already if they are concerned about future generations, but unlike the normal situation there is no longer an intermediary adult child/parent through whom assets can pass. It's a hard situation to define because the law hasn't gotten that far. You might say that biomedical science can divorce the person from reproduction but estate law is intrinsically about the person, their property, choices, and family; how do these reconcile? It requires forethought on the part of the planner.