Why should a primary child need to make soup? It ought to be a few years before they are fending for themselves, I hope.
@Min, for the same reasons that they ought to learn how to ride a bike. It's about teaching life skills, which hopefully improve as the children get older. My 7 year old son can bake biscuits and cakes, and does quite a good fried chicken in soy sauce...
Kids learn that food can be cooked easily at home, and does not require parents to make it for them always, or a trip to 'Mickey D's' or similar. Personally I'd much rather they learned to cook rather than be heating up microwave ready meals from supermarkets or relying on take aways when they grow up and leave home.