In a study conducted by Penn State University and published in the journal Psychology & Behavior they discovered that about 1 in 4 people is a 'supertaster'. In short, a supertaster is genetically enabled with taste sensitivity that may be 10 to 100 times more acute than others. In other words some folks will get a very powerful reaction to tastes that others will not. They did note that supertasters tended not to like foods that were identified as bitter in taste like broccoli or some cheeses. Applying salt to bitter tasting food effectively masks the bitterness and makes the food more enjoyable. While some people react mildly to a slightly bitter taste a supertaster gets a powerful negative reaction. You can read more about supertasters at this Science Daily article.
So if your child is a chronic picky-eater it just may be she or he is a super taster (and a salt lover)!