it was like I was a detached person just watching myself go through the motions of life.
Yes, it is something like this.
I think you are much like me in this regard - you know yourself well and if this does happen (hope not), you will have a very good baseline of your own normal. I think it helps.
Also think about talking to smallsteps maybe? I don't have kids, but I still remember from the kid side of life, but I was a lot older than she i now I was 16 when my mom had her stroke, and the understanding was never there for me.
She will grow with you regardless of any conversations you have, perhaps there will be more to voice their thoughts on how much to tell a small kid, maybe someone that remembers from being small.