Feeding issues are always the most contentious!
My own opinion from reading both sides of the discussion over a few years now is that puppy food is not necessary though some like to feed it. Lots of us never feed it at all. I don't and never recommend it.
Many breeders especially in the US do not feed it to their puppies and will not recommend it to their owners -- indeed for many breeders (such as Roycroft's Laura Lang) it actually violates the our terms of contract for adopting a puppy, to feed puppy food. This is because many feel puppy food is far too high in protein and nutrients, accelerates growth, and can contribute to bone and joint problems later in life. It is known that accelerated growth can cause serious problems for large breeds. Whether this holds true for small breeds I do not know, but personally I feel at best puppy food (except for underweight pups in poor health) is just a marketing ploy. So is kitten food, for that matter. Most cat breeders I know of also will not recommend kitten food. So there are strong differences of opinion on this as with many types of feeding issues.
Consider that once canids are weaned, the parents do not feed them a special diet for the next 6 months to year of their life! They simply eat what the pack eats. Likewise children do not need extra high levels of nutrition in their food. They will as they are growing, generally eat more food than adults and just need healthy diets (sadly something fewer and fewer kids seem to get these days...).
I'd feed an adult food in the same amount as a puppy food -- and be aware most puppies will gradually eat less anyway (mine all dropped from about a cup a day to somewhere between 1/3rd to 3/4ths of a cup of food, US measure).
For more info on feeding puppies and adults cavaliers, scroll down this page from cavalier breeder Laura Lang:
http://roycroftcavaliers.com/manualfeeding.htm
For the average home I think the best and most balanced diet for a dog is a primarily dry food based diet (NEVER only soft food -- this is setting the dog up for very poor gum and teeth health which i turn leads directly to higher risk for heart disease) -- supplemented with *real* food such as fresh meat, veg and fruit, occasional tinned or prepared raw, etc. There are lots of suggestions on healthy feeding in the Library section.