Trust their competence in a given domain, yeah. To take a non-IQ-related field, I would have said "It's fair to assume a six-year-old, or even an adult, doesn't understand much about economics and therefore their opinion of it is worthless. Most don't. And that's okay, because if I need to prove I can explain it, I'll just do. And then they'll trust my understanding of it and listen to the opinions I base on it.".

And that's true to an extent. But an adult can pick up so much cheap credit condescending to children that they just don't start trusting them. If a kid demonstrates their understanding of economics to an adult, the adult will praise the child, but not even think that the child's opinions on economic policy (as opposed to, say, a pundit's) should carry any weight.