I know someone who has a young child who is very likely to die in the near future. This person has (most likely) never heard of cryonics. My model of this person is very unlikely to decide to preserve their child even if they knew about it.
I don't know if I should say something. At first I was thinking that I should because the social ramifications are negligible. After thinking about it for a while, I changed my mind and decided that possibly I was just trying to absolve myself of guilt at the cost of offending a grieving parent. I am not sure if this is just rationalization.
Advice?
because the social ramifications are negligible.
You should reconsider this assumption. I would imagine that making suggestions about what to do with someone's soon-to-be-dead child's body would be looked upon coldly at best and with active hostility at worst. It's like if you suggested you knew a really good mortician; it's just not the sort of thing you're supposed to be saying.
There's also the fact that, as a society, we are very keen when watching the bereaved for signs they haven't accepted the death. To most people cryonics looks like a sort of pse...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.