They feed the children early and have them go to bed before the adults eat with linen, silver, and china. This is certainly different from our family where children are welcomed at every meal and meals are usually buffet style on paper plates. One son's wife grew up in Asia. Her language, many of her customs, a few of her values and even her religion, are totally different from ours. Yet, we have all learned from each other and my grandchildren have the best of two worlds with combined cultures and values.
Children are adaptable and can always roll with the punches.
However, it is wise to talk to your children about the rules, regulations, cultures, and values they choose to use in raising their children. They choose and you remember that it is their choice, not yours. It's also important that these choices be respected by the various relatives. Substance abuse or other dysfunctional traits should be confronted, though, regardless of the unpleasantness involved. These are your grandchildren and they deserve your help for a normal life.