[Minor49er]

If it's for your children, why does it need to exist digitally for 100 years and not, say, 20?

The solution is to print out your writing, put the pages in plastic sleeves, and clip them into binders. Keep the copies in filing cabinets in separate physical locations. It's a one-time cost that isn't subject to digital media issues. You can't accidentally delete the writing or lock yourself out of an account that stores the files like you can with a digital copy