Lots of “teaching” is literally excluding from consumption for young kids. Parents know better than their kids, why entrust that kind of advanced decision making within them?
> why entrust that kind of advanced decision making within them?
Because then there's a hope that they'll actually learn the underlying principle and make similar decisions in situations where someone else is not directly in control of their behavior.
There are kids who don't get to eat ice cream before dinner at home because that's the rule, who will happily do so when over at someone else's house without their parents around to enforce that rule. Then there are kids who actually understand why they shouldn't eat ice cream before dinner, who will decline to do so even if they have the opportunity. (That doesn't mean they'll exercise perfect judgment every time, but then, there's also no guarantee they'll follow rules that aren't being enforced.)
It's important to develop the critical thinking skills to filter out "junk food" content.
(To clarify: I'm not talking about children too young to understand the concept, I'm talking about children more than old enough to make such decisions in an informed way. Roughly speaking, think 12, not 3.)
