is actually an evolutionary good thing.
Also, not a scientific survey, but I have noticed that parents who claim their children eat everything are usually not right about that.
Years ago I had a child development book by Penelope Leach, who used to be a big name in the field. In it she analyzed the typical diet of about four or five different toddlers whose parents had come to her expressing grave concern that the kids weren't eating right. All but one was perfectly fine, and the one that wasn't (kid would only eat white bread with butter, as I recall) Leach realized that this was simply a stage the child was going through, and soon enough would be eating other things.
Most adults themselves are far pickier than they realize. Especially vegetarians and vegans. Not to mention that even the omnivores among us have strong likes and dislikes. Then there's the inclination in this country to assign magical powers to certain foods, accompanied by completely unrealistic claims about how phenomenally good or bad one particular food is.