Parents vs. Grandparents
This is the eternal struggle between those people of different generations. They are people of different generations and they are people of different points of view to this life that is why it is sometimes hard for them to find the mutual understanding, especially when it is about kids.
Parents are usually stern to their kids because they want them be obedient and they want them realize all do's and don'ts of this life, though grandparents usually let children do a lot of things their parents forbid them to do. And this is where the problem starts. That is why they usually quarrel about kids and about the best way to bring them up.
Parents believe that grandparents spoil kids when they let them do things that are forbidden at home. And they are actually right. Grannies don't be too kind towards your grandchildren. Let your kids make their own choice about rising up their children. Never stick up your nose into their business, be just grannies but never be the opposition for parents.
With such a behavior you rally spoil kids and you make them believe that their parents are not that smart and it is okay to neglect their opinion. In other words you make your grandchildren disrespectful towards their parents. It is wrong.