I don't see how this relates to regulating a child's junk food intake. Do you think companies should decide what we can buy?
I think the point is more that just because people seem to prefer a product at first glance/first use doesn't mean that that's the product they will prefer in the long run.
Something like the pepsi challenge ( http://en.wikipedia.org/wiki/Pepsi_Challenge ), if people are given a sample of pepsi and a sample of coke and not told which is which, they generally prefer pepsi if they just take one sip because of the extra sweetness, but if they drink a whole can of each then coke (the less sweet beverage) is usually preferred.