This brings back memories, grrr.
When Dd was 10 days old my ILs came to visit. MIL INSISTED that a new mom needs to get out of the house. Impressionable new mom that I was, I actually agreed to let her take me to Wholefoods for an hour.
My heart was breaking as she tucked Dd into a little baby chair gift we'd been given, and FIL sat on the couch across from the chair. I explained to him how to use the cloth diapers, and he said, "Oh, I'll just let it wait until you get back."
I almost said, "that's it, I'm not going." Instead, I said, "When you're ancient and senile I'll change your diaper if we're alone and you need it, I expect you to treat my daughter with the same courtesy." He actually took a look at the diaper, figured out where the velco attached, so I felt like I could leave.
I used MIL's cell phone to call him when we got to the store, and he said that Dd had made a Huuuuuuge explosive poop - and that he had changed it.
Aside: I was so glad to get home that day, I NEVER let anyone talk me into leaving Dd "for my own good" ever again.
But what it comes down to is no diaper changes, no baby. If grandparents feel like they've changed enough diapers in their life, they can enjoy the baby while parents are around, but cannot babysit.