Does Atticus think a jury of children would have found Tom Robinson innocent?
There is every reason to believe that if the jury was made of only children, Tom Robinson would have been declared innocent. Atticus knows this, and the reader knows this. There are at least three reasons to support this point.
First, Atticus delivers a brilliant performance. He cogently demonstrates that Tom Robinson did not beat or rape Mayella. In fact, physically it would have been nearly impossible for Tom. Moreover, there was significant evidence that Bob Ewell could have done this terrible deed. So, from the evidence itself, Tom would have been declared innocent in a bias-free or hate-free context.
Second, if we look at how the children viewed the trial, it would be clear that they strongly believed that Tom Robinson was innocent. Here is what Jem says to Reverend Sykes: “He’s not supposed to lean, Reverend, but don’t fret, we’ve won it,” he said wisely. “Don’t see how any jury could convict on what we heard—” From Jem's words, the decision is absolutely clear; Tom is not guilty.
Third, children are innocent. They have not lived long enough to imbibe the hatred and racism of the world and Maycomb. So, if facts are laid out, they would make a better decision. Maycomb, on the other hand, is blind. And what guides the jury is their blindness.
There is a quotation that would help my previous answer. Let me post it here. Atticus says these words to Jem:
“If you had been on that jury, son, and eleven other boys like you, Tom would be a free man,” said Atticus. “So far nothing in your life has interfered with your reasoning process. Those are twelve reasonable men in everyday life, Tom’s jury, but you saw something come between them and reason. You saw the same thing that night in front of the jail. When that crew went away, they didn’t go as reasonable men, they went because we were there. There’s something in our world that makes men lose their heads—they couldn’t be fair if they tried. In our courts, when it’s a white man’s word against a black man’s, the white man always wins. They’re ugly, but those are the facts of life.”