Basically, it’s partly parenting and partly genetics, according to Slate.
Children who are picky eaters aren’t just giving you a hard time; many of them are exhibiting “relics of an evolutionary survival tactic: Animals old enough to forage for food alone but too inexperienced to know what’s safe are less likely to accidentally poison themselves if they are cautious about trying new foods.”
Plus, children who exhibit food neophobia — wariness of unfamiliar foods — may have genetic differences behind their fussiness, or may have had nerve damage from middle-ear infections, which afflicts three-quarters of children by the time they’re 3. This infection can damage the nerve that carries taste information from the tongue to the brain, potentially making certain foods, like cauliflower and broccoli, taste more bitter.
But researchers have also found that parents can make innate fussiness much worse, and that instead of punishing children for not eating their vegetables, which then can become associated with stress, parents should reward children with non-food treats, such as a sticker for each bite of disliked food.