I have two kids. If left to their own devices, they would eat the tastiest things on their plate, then stop (then complain about being hungry an hour later). They would never eat anything remotely healthy, and subsist entirely on chocolate if given the choice.

Since we have evolved to value fat and sugar as being the tastiest substances, children do have to be taught/persuaded to eat healthy food.

They also do need to be told when to go to bed. The times at which we have tried to let them set their own bed times have resulted in them trying to stay awake as long as they possibly can, until they fall asleep in the middle of whatever they were doing. They almost never voluntarily go to bed, no matter how obviously tired they are.

Eat a meal with a family with a single child. In many cases, the parents will spend much of the meal ordering or pleading with the child to eat their food. Then eat a meal with a family with 6 or more children. That probably won't happen.

I do know one kid who really won't eat on his own; if you don't coax him into eating, he won't eat enough. But that's unusual.