I could have actually written your post emlu as I am eldest of 4 too, with my dad and stepmum utterly uninterested in my 3 DC despite them being their only GC so far. Nearly everything about your post is the same as my situ.
It is very hurtful, I used to live round the corner from them and they never ever dropped in etc, I did drop in on them but gradually stopped because it is possibly even more hurtful to turn up (sometimes announced, sometimes not) and they would all carry on with what they were doing, not really wanting to talk. Leaving me with DC, ignored, feeling like a prat 
I echo a previous poster- sometimes it hurts more to want something that people just can't give you, for whatever selfish fucked up reasons they may have. My dad and step-mum also don't see my Dbro, don't even bother to try with him despite him going through a rough patch. They say awful things about him, conveniently forgetting that they haven't made effort with him through most of his life, now he is an adult he has chosen not to bother with them, and HE is the bad one?! Ridiculous.
I always think I should stop thinking about them, and just leave it. But I know it is going to really hurt when my half-siblings (who live with them) have their kids etc, because then I just know that my Dad and his wife will be totally involved with them.
I think the final straw happened when my 3rd DC was born 7wks ago.. They planned a holiday abroad across the 2wks of my due date, came to 'see' my newborn when they got back, and my dad literally did not even look at him properly. he walked in, glanced at him, they gave my other 2 DC presents which they boasted had cost 49p from HomeBargains (I dont care about the cost, but why say it in such a crowing manner?!) and then left after 20 awkward mins. Horrible.
Do you have any close friends to talk about it to? I'm lucky that my mum is obviously divorced from my dad, and hse would walk over hot coals just to spend 5mins with the dc
so she is a lovely grandparent.
FWIW, I think your DC will be fine without close Grandparents, they can't miss what theyve never had, can they? Not in any damaging way I dont think. And it is not your fault that your parents are morons, such a shame people like us have to walk around feeling sad and awkward about it though.