If we assume cryonics requires advances within the century, it's still true that those advances are more likely to come LATER than sooner. Cryonics means I survive whether the advance comes tomorrow or the day before the company would have thrown in the towel.
So the odds still favor the cryonaut over the African kids, because the cryonaut has longer for that advance to occur. Also, the cryonaut is someone who has the resources and culture to invest in a long-shot like cryonics DESPITE it being unpopular and fringe, whereas the African kids are unlikely to do any such thing. The African Kids only survive if there's a massive world-wide change like the Singularity or Friendly AI.
Keep in mind, we live in a society where millions die of starvation simply because we're inefficient at distributing food - we have enough to go around, it just doesn't end up where it's needed. We're talking a VERY radical change, and it needs to be before most of the kids are already dead (if it happens in exactly 60 years, statistically most of the kids are probably already dead)
I am not currently signed up for cryonics. I am considering it, but have not yet decided whether it is the right choice. Here's my reasoning.
I am very sure of the following:
1. Life is better than death. For any given finite lifespan, I'd prefer a longer one, at least within the bounds of numbers I can reasonably contemplate.
2. Signing up for cyronics increases the expected value of my lifespan.
But then I also believe the following:
3. I am not particularly exceptional among the set of human beings, and so should not value my lifespan much more than that of other humans. I obviously fail at this in practice, but I think the world would be a much better place if I and others didn't fail so often.
4. The money it would take to sign up for cryonics, though not large, is enough to buy several centuries of healthy life each year if given to givewell's top malaria charities. Since on average I expect to live another 50-60 years without cryonics, the investment would need to increase the expected value of my lifespan by at least 5,000 years at minimum to be morally acceptable to me.
5. There is a chance we'll discover immortality in my lifetime. If so, then if I signed up for cryonics the payout is 0, and the people who died because I bought insurance instead of charity are people I could have saved for far longer.
So, what do you think is the probability that immortality will be discovered in my lifetime? What about the probability that, if signed up for cryonics, I will live into the far future? These priors would seem to be the key for me to decide whether signing up for cryonics is morally acceptable to me.