Is it right that a parent refuses their child to see his grandparents? what emotional effect will this have on the child?

In an ideal world: In an ideal world we would all "get along" and children benefit greatly from having contact with all members of a healthy extended family. When we fall short of that ideal, it's important to look deeper at family dynamics, starting with our own roles. A family therapist can be extremely helpful in starting a healing process. It can help the whole family, especially those children.