There are all sorts of reasons why manners are important, and now that the Junior Gastrognome has just passed his eighth birthday (a point at which he gets the privilege of scraping not only his plate, but everyone else's - next year, clear the table, the year after, stack the dishwasher), I understand at least one reason why manners should be imposed on a child. The French have the right word for it, which is sortable; that is, without manners, you can't take the kid out. And that is a bore.
If you look at this subject soberly, however, you will note two things that children are quick to realise: first that many grown-ups do not display the designated manners (they will talk with their mouths full, they do put their elbows on the table), and second that many of the prescriptions are not only boring, but really don't make that much sense. To the former, one can point out, at least to a sophisticated child, that a bad priest is no reason for abandoning a religion; but to the latter, the answer is more difficult. If grown-ups, at least at home, put their elbows on the table, that is because it is comfortable: especially had they been, like the child, spending a weary day conjugating the future of etre and avoir. Practicality would say that a napkin is handier by the plate than on the lap; it can be brought into service more quickly. And when, if you're hungry, is a mouth not full and available for words?
Putting myself in Master Junior's place, I can see a goodly number of reasons why many of these rules seem arcane and discommoding. But it falls to me, not my wife, who is a stickler on such matters as the French bourgeoisie generally is, to explain why the rules should none the less be observed. My explanation generally is - and I illustrate it by flapping my elbows wide like a chicken and bumping his rib cage - that manners are there as a means of promoting general civility. I will then explain that if his mouth is full, I cannot understand what he is saying (I am good at imitating a donkey with an apple in his mouth reciting Homer). The elbow- prohibition is another matter. As he is an uncle many times over, and in my family uncle-status allows elbows, I have to give him a wink, which he interprets (rightly) as, "You know how your mother is".
But I went through the same drill in my childhood. My mother was far fiercer, too. Why, I was not even allowed to sop up delicious sauces with a piece of bread! That was what peasants did. Ugh! She was, also, adamant, like any well-bred Italian, that fruit must not, under any circumstances, be eaten with the fingers: one peeled it on one's plate with a knife and fork, cut it up and put appropriate-sized bites in one's mouth.
From which I concluded that manners are a skill; and that if you want to have a certain station in life, you must preserve the manners and customs of the past. They are not unlike going through a marriage ceremony; not strictly necessary, but more decorous. Thus has civilisation ever preserved itself: by enforcing its rules on the next generation. And when you think about it, civilisation is right. Not to have your napkins on your lap is just the start of a slippery slope. So, kid, don't talk when I'm talking. And no, you may not get up from the table until you've finished what's on your plate