I'm sorry you feel like this @AmateurOwls
but please don't let them know how you feel. Mine say they don't want any kids either - 2 DC both 30-ish/close in age .... Left home a decade ago, and have University degrees and are successful professionals, and they travel quite a bit - for pleasure and for business... Having a baby is the last thing on their mind. A baby just wouldn't fit into their lives at all ...
I see women my age (and some 10-12 or so years younger - and a few a bit older than me,) who have fairly recently become grandparents, and every now and then, I feel a pang of slight envy,... My 2 BFFs (2 to 3 years younger than me) have become grandparents just this past 2 years, (1 grandchild each,) but the situations with their daughters are not great. In both cases, the daughters split with the baby's father, soon after the baby was born, and they and the grandchild have moved back in with my friend(s.) I sure don't envy THAT!
Your kids may change their mind, like mine may do. But they may not. I would just make peace with it now, and be very happy you have got healthy and successful adult children, and a husband, a decent life, nice holidays, and friends etc.... 
Then if they DO come to you and say 'you're gonna be a gran!' it will be a bonus.
I would be thrilled if one (or both) of mine came to me and said they're having a baby, but I won't be devastated if they never do. My health and happiness and well being and future happiness does not depend on having grandchildren. If they come along - ever, I will be thrilled. But if they don't that's OK too.
As I said, my DC may change their mind.
But they may not....
It's OK to vent on here. You're allowed to feel how you feel. 
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