I find it interesting that you say all kids love to spend time with their grandparents. Ummmmm...my brother and I are an exception to that. My mother's parents weren't comfortable around kids at all....and both of them were unapproachable to both my brother and I as children, we hated visiting with them....HATED it.
My Dad's mom....well, there's a reason she's referred to as "grandmartyr". My father never had a good/loving R with his parents and well....honestly while I did quite a bit for my grandparents....that's another R I would definitely not refer to as "Loving". My grandmother makes it very hard for you to even like her. My grandfather OTOH I do remember quite fondly, he was a very non-judgemental type person (in my eyes)....but never said much and was never physically affectionate. I don't ever remember even being hugged by him.
My brother and I (sad to say) truly didn't look foward to the times that we spent with our grandparents. I would say that I never really had any type of an R with mine....until I became the person who was responsible for their welfare in their declining years (my other grandparents died while I was still young.)
In some ways I envy those people who looked forward to grandma & grandpa visiting. Fortunately, my parents and my H's parents are much more approachable and fun for our S! GEL