People would be beyond brilliant and would be approaching levels of genius never previously achieved by mankind. The one thing holding humanity back is its constantly being subject to lies, evasive answers, sarcastic and conflicting answers. If not for those smart Alec responses to good questions, flying cars, cold fusion, and the meaning of life would all be solved already.
Giving people misinformation isn't exactly what affects their brilliance. The thing that matters is that they are taught (preferably during childhood) to always use critical thinking. Then they can find out on their own when something is true or false/valid or invalid. For example, a philosopher, like Socrates, would have been given plenty of " lies, evasive, sarcastic, and conflicting answers" in response to his questions, but because he was a philosopher, he knew how to call those things out.
I think that misinformation can be a great thing for children, because it teaches them not to be gullible, and to think on their own. I was quite the thinker when I was little, and that was probably because I had to. If all information is handed to them on silver platter, they won't learn to think and learn for themselves. I think this is one of the reasons that I'm as smart as I am.