When I was a judge on the mental health calendar, one of my happiest collateral duties was to officiate over three adoptions almost every morning, and I tried to make them the truly special occasions that they were.
So, among other things, if there were grandparents in attendance, I had them raise their hands and be sworn, right along with the parents, saying that they had duties to perform as well. Then after complying with the law and having the parents swear to support the children and treat them just as if they were their natural birth children, I also figuratively had the grandparents swear that they would spoil the grandchildren. And I never had a complaint. (For example, of course, the child can have a chocolate chip cookie before dinner, etc.)
Being a grandparent is a wonderful thing. Yes, when the children are messy or misbehaving, they can mostly be returned to the parents, and that can be nice. But much more importantly, the relationship between children and grandparents is truly special.