1 grandad of mine died years before DD was born, but the cemetary is near our house so DD often came with me to visit his grave there. She also got to know her other 3 surviving great grandparents on my side - 2 of whom have died in the past 2.5 years (and the last is very frail so probably won't see Christmas). For both, she came to the Church for the removal, but not to the funeral service - and has visited the grave of that Grandad and helped to scatter Grans' ashes from a boat onto the sea (Gran's wishes). DD is 6 and has Aspergers, so things are taken very literally.
She also talks about them still a lot - and the fact that they are gone and won't be back, so it's sad but it was lovely to get all the hugs from them while they were here. And she does talk about heaven too.
It also means that, while we have to be careful to explain things very literally to her and not use the euphamisms that many people do (she didn't "go to sleep", she "died"), it also means that she is aware of that circle of life and that everyone will die at some point. (Occasionally, she talks about when she is grown up and that I will be dead - but not in a morbid way, just very matter of fact).
It also means that I don't have to hide things from her. So if I am sad about my Granny who died, I can cry cos all grownups cry sometimes. And they can remember happy things about the people who died too. And if I am worried about my other Gran, I can say that, and that I know she'll die someday, but probably not today (certainty is important too in our household, which is not always possible on such subjects).
When my 2nd Grandad died, my siblings and I were all there as we are adults, but his other 3 grandkids were still under 10 (their dad was the youngest, my dad the eldest) and their parents couldn't deal with it all and sheltered them entirely from it - so they didn't know how to react (all the usual taboos etc), meanwhile, I just brought DD along as we had no alternative in the evening, and she saw it all (not open coffin but the service and lots of chat afterwards) so it was nothing to be scared about or not talk about.