Should grandchildren know?

Personally yes I do think they should be told, any details can come as they get older and ask any questions but I don’t think we have the right to wipe someone existence out just because we don’t have them in our life
You don’t say how old the child is but I remember my grandkids loved simple family trees when they were young after all it’s their history isn’t it ?

As my DGC have grown older they have asked about DS's father and my ex. I simply told them he does not live near any more and they accepted this. Sadly one DS told his DC he was not a very nice man, which is true but in my opinion too honest for them at their young age.

I think they should know ,just that he doesn't live with you and doesn't see family ,but they should know of his existence

DHs dad died when he was young. My MIL and Step FIL are Nanny and Grandad but we don't see them anymore.

Both of the children know all about this, they know of them and the situations why we are in them. As child friendly as possible. I think at this age they focus on what they have rather than what they don't have.

My dgc aged 9 and 6 are aware of our similar situation.

I am a step granny. A few years ago when little the eldest asked about when her daddy was born. She was told that daddy had another mammy that now lived somewhere else and I was a special kind of mammy.

She was totally accepting of this as I am all that she knows and younger brother just followed in her path. It didn't bring up any ideas of mummies disappearing or going away. They know that I am not daddy's real mammy.
I am still treated as their granny.

Mum and dad spoke with minimum of fuss and it was all very matter of fact i.e. Can I go on my bike now

I think there's a difference between "You have a grandad whom you never see" and "Granny had a husband who doesn't live with her any more".

The first one could give an impression to the child that they are missing out while the second makes it more vague and less concerning to them.

I don't think so tbh. Depends how old the child is? Young children don't actually know how grandparents come to be or what the relationship is to mum. For example, my husband is not biological 'grandad' he's just grandad anyway and some of my GC have more than two grandads (grandmas marrying twice or more) They are ALL grandads, but I suspect the kids just think they are old men ha ha. They don't understand the connection.

Once the kids are old enough to understand the family tree scenario then maybe its appropriate? Only you can decide. But for young kids I would say NO, don't complicate things.

Let their parents mention this when they think they are the right age.

I think I would agree with vampirequeen
Although children do tend to question even from a very early age,
so if your DGC is told of his existence be ready for the 'but why' type questions.
The grandfather even though not on the scene is still part if their family tree as are his forbearers.

I think they should just be told in passing. They may be interested for a short period of time then they'll simply accept it as the norm. It's easier to let them grow up knowing that he exists than have it suddenly sprung on them at some point in the future.