There’s a few dynamics at play here that requires respect and control of entitlement on both sides. BUT (having come from and married into) a loving and supportive family I never understand the double standard of ‘you decided to have kids so need to not be anyway entitled about help with them from their grandparents’ vs what I believe to be a lifelong commitment to help and love and support your children. Your grandchildren are maybe not your responsibility but by default they are. You decided to have children and that doesn’t end when they are 18. I think it’s ok to expect your mum and dad to still be supportive.
Of course as the adult child of someone you also have a responsibility to not make your parents unwell or take so much from them that it damages their quality of life. And to also support them with help and love and consideration.
I guess some people don’t make the jump to grandparent who still feels love and responsibility for their grown up child, and grown up child who doesn’t realise they now have a responsibility to care for their parents.
But my AIBU is, if you have a child I think you are taking on the responsibility of being both a parent and a grandparent (probably) as part of that. And don’t get to just wash your hands of the role any more than you get to wash your hands of being a parent. (Assuming you haven’t raised entitled dickheads for children).