I am a child (well, I'm an adult now
) who had no grandparents. DF's parents passed when I was very small (less than three) and DM was NC with hers. Neither of my parents had siblings so it was just us (my parents, me, and my two siblings).
I do and I don't feel like I missed out. Apparently Df's parents were lovely, and me and my grandmother share a couple of interests and it would have been wonderful to have met them and shared that experience. I wish I had that, but not in a yearning 'I feel incomplete' way, it's a bit more detached than that, if that's makes sense.
On the other hand I can't really miss what I've never had. It's not like I had grandparents who were suddenly taken away from me. It has just never been a reality in my life.
I suppose I could compare it to travelling. I might really want to visit India. I might read up on the history and culture, talk to people who have lived there or have visited, and got a real sense of the place and wished more than ever that I could go. I might feel sad that I haven't had the opportunity but I don't miss it. I don't crave the feel of the sun on my skin, the buzz of the cities, the sights, the smells, the tastes. I'm bloody knackered so this probably makes no sense 
I feel for you, deeply. Not only are you missing your parents (and I'm so sorry for your family's losses), but you are missing what your DC could have had. But although they may miss it when they're older, it won't be in the same way as you because they don't know any different 