why do scout and dill go outside?

The children leave the courtroom during Tom Robinson's testimony. Dill is distressed at Mr Gilmer's angry response to Tom saying he 'felt sorry' for Mayella Ewell. Dill begins to realise that Tom has no chance of a fair trial with the depth of prejudice which is tangible in the courtroom. He is aware then that Tom will be found guilty because of his pity for Mayella, not because he committed any crime. Scout takes him outside.