system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are younger children so picky about the foods that they eat?
gpt
I remember having a course on evolution and behaviors where we were taught that children are picky with vegetables because in nature, a lot of plants are toxic and children tend to avoid them, especially since children are more fragile in case of an eventual poisoning. Moreover, a lot of green vegetables have a bitter taste and this tends to be an indication of toxicity in plants. As adults, we lose our sensitivity and therefore our aversion for bitterness, and we just learn what is safe or not to eat.

Add to that some other factors, like cultural aspects (advertising for instance, fastfood restaurants), or the fact that humans have a natural tendency to favor energy-rich food (for evolutionary reasons that are not really "useful" anymore when you live in a developed country).