My DS1 (aged 3) has never met my mum, as she died a couple of years before he was born.
A few days ago we were looking through some albums and I came across a picture of my mum, and he said "who's that?" I explained that it was my mummy.
I wondered if he would ask where she was, but he didn't. However I think it's only a matter of time before he puts 2 and 2 together and realises that Daddy has a mummy, who is here, and Mummy's mummy isn't.
My mum was and is a very important part of my life, and I want to talk to my DC about her, and make her a real person to them. But I don't know how to go about this without introducing the idea that people's mummies can die and go away forever and never come back - I don't think they are ready for this.
I would be interested to know how other people deal with this? We are not religious which makes it harder - I can't say "she's in heaven" (or at least not without feeling a big hypocrite).