I lost both my parents by the time I was 20. When this has happened to you, it's impossible not to think about it. The best thing you can do is prepare for it as much as possible and then forget about it and get on with your life.
Ensure you have substantial life insurance so that whatever the eventuality, no one needs to worry about money.
Make your wills and appoint guardians, although this may be something you may need to revisit and change as your child grows. We are on our third set of guardians.
Write down milestones and memories and make sure you are in photos, not just taking them.
If you don't have a strong wider family, build a strong circle of friends.
This will not be what you want to hear but unfortunately, I have been diagnosed with a terminal cancer (an incredibly rare cancer and in no way hereditary) so history is partially repeating itself for us.
What brings me, and my teenage children, comfort is that I have always been able to be there for them, first as a SAHM and then working around school hours and as a family we have been able to enjoy "the small things", putting that above money and really have always tried to make the most of every day and never put stuff off.
But they are our family values. Everyone is different and everyone should think about how they want to live their lives, not how society says they should. By doing that, even though I haven't quite got my 15 yo "over the finishing line" I feel like he's got enough of the important stuff from me and my 20 yo has already said that he knows he'll be ok because the same thing happened to me, and I am ok.