Parents must discipline their children. That means they must give the children orders. For example, "Don't run when you are carrying a knife." The order is correct, but the child views it as just another of the many orders he/she receives daily from their parents. Grandparents usually take time and show concern and love for the child, so the grandparent may say, "Oh sweetheart, don't run when you are carrying a knife because you might fall and the knife might cut you and it will hurt a lot." Even young children recognize that grandparents are wise, so together with an explanation and an expression of love, the child may respond better to the suggestions/recommendations from the grandparent. What do you think?

It depends on many things. I suggest you to ask your question in DISCUSSION part. It seems suitable.