in our today's environment with refined foods and lots of pufa and other toxins in them, yes eating like 6 year old maybe is not that healthy sometimes.Eating like a six year old and 'babies know best' is just a flawed concept.
If you put a pipe of pringles (which only nuts or drinking oils can rival for its PUFA content) in front of a child, and they will munch their way through the entire pipe.
Sure, they'll wash it down with some coke if you give them that as well.
If you put party food out in front of kids (PUFA soaked sausage rolls, pastries, crisps, cheap pizzas & commercially made disgusting cakes) and watch the feeding frenzy before you. Happens every day of the year in homes everywhere.
There's nothing instinctive about 'eating like a six year old' being 'healthy'. But there is an instinct of a 'need' for sugars. That's about it IMO.