has ur son brought up death before?
do your parents live close by so you guys visit all the time? do your children see them regularly?
also each child is sooo different. there is no one rule that applies to them. so it is not necessary that every child thinks that just because someone died from sickness that its going to happen to them.
if death has come up before then it will be a little easy for you.
if you guys live closeby and he is close to his gparents then he will pick up by just watching. the best gift you can give him is to visit both gparents regularly and often. seeing gpa in hospital will be the best way to do it.
talk about gpa first. tell him gpas heart is not working well. the doctors need to fix it. so he will be in hospital for a while and then recovering at home. and then visit him in the hospital.
from the age of 4.5 to 5.5 my watched and took care of both her gpa and step gma slowly die at home. i was their primary caregiver living with them. she loved both of them dearly and took part in everything - from helping them, to holding their hand while they passed, to reading and singing to their body while the adults did the phone calls, washing and dressing them. it really had a big impact on her and definitely, definitely, definitely helped her with her grief. something which her dad didnt have to deal with till in his early 40s and he struggled with it. for two years afterwards she would cry at all different moments whenever anything reminded her of xfil or xmil.
when i went to live with them i cant even remember what i told my dd. if i even had to speak to her. since she stayed in such close touch with them she could see them getting worse. we had already explored death in great depth.
i never read her any books. like in your case dd had enough examples IRL.
and the key were her questions. i never found a book dealing with her kind of questions. and when i didnt know i expressed that myself. if i was ambivalent i told her that too.
mama. that's quite a bit to be dealing with all at once. since your son is so perceptive i would say have the talk as soon as you can because he is picking up so much from you all.