I guess grandparents are parents, too...
My folks were both only kids. They really didn't have a clue how manipulative younger siblings can be and frequently fell for my younger brother's stories.
Their parents, all four, were born into families with lots of kids and three of the four had been the youngest. They were not exactly clueless...
So one day my brother and I were dropped off for a week at my dad's folks. I did something which was not considered a big deal to my European relatives (took a piss in the compost patch with the gardener) and my brother, assuming I'd be judged by American standards, ran to tattle on me.
O, dear. My grampa was just shocked. Shocked, I tell, you - shocked. He agreed with my brother that the matter was grave indeed and a suitable punishment must be found. Hmm, no gelato for a snack? Would that be adequate? Hmm, my brother obviously considered this weak justice, indeed, for the seriousness of my crime.
Well, grampa went on, perhaps no TV the whole week? Ah, my brother opined, far better, but no ice-cream, too.
But of course grampa answered...and promptly pronounced the punishment on my brother for being a tattle-tale.
Tee-hee.
Nothing in my life tasted as good as all those gelati that hot week in the middle of summer. I'm not a big TV fan, but I watched more that week than ever before or since.
Of course, when our folks picked us up, I got in big trouble on the way home cause my brother couldn't wait to tell all.
Leaving out our grandparent's sense of justice of course.
From that day on, we had two sets of rules in the family. I loved visiting the relations, my brother somewhat less.