I don't think that it should be forced. A child should be allowed to eat as much as they want (if family can afford it) and eat whenever they want. Looking back at my childhood and what my parents told me about theirs, young people should explore the world and should not be bound to "manners". If a child doesn't want to obey, they will ignore the "manners" anyway. I don't think you can force it. (Unless you beat them senseless)
mother cooks so that when the Dad gets home dinner is ready and you can all discuss the events of your day.
I dont see why exactly the mother should cook and the father work. He can cook too. She can work too. The children can cook too. Ideal is if everyone cooked and everyone worked. However the most important thing is that the family approaches the way everyone is the happiest with. If the family does the old "Mother cooks, dad works, children do nothing" please only do it with everyone's consent.
Also I don't understand why events of the day have to be discussed at dinner. Let's ignore the fact that not all families can do that (nightshift for example) for a moment. Family members should be able to discuss their events at any time with anyone anywhere. You should not be bound to such imaginary boundaries called "manners".