My daughter was 6 when she found me convulsing on the bathroom floor, she ran down stairs shouting call an ambulance, my wife had to leave her with a neighbour and when she returned she told her the one and only untruth, that I would survive
I think I would have felt the need to protect her but my wife, a head teacher took the opposite approach and told her everything, I have to say it worked.
So she learned about the brain and how it can bleeding and rewiring occurring over time, so she understood it would take a long time before the dad she knew returned.
Before her A levels she was going to be a Neuropsychologist, however she's taken a totally different path at Uni and loving it.
It wasn't all easy, as after my bleed I was unable to interact with her in the same way, when she was 7 I can vividly remember her asking "Do you not love me anymore".
Tough but we both survived and by again explaining plasticity it help her a lot. Kids can be remarkable if they're not confused.