Encouraging discussion in history with your child may be easier than you think. In any history reading, there are certain facts to know. Who did this? What happened? When did it happen? However, there are also elements to the story that may not be clear. These elements are up to the person's interpretation. Why do you think it happened this way? Do you think this was a good thing? Was this good for everyone involved? Were the people right in going to war? Asking the why questions and the questions that involve judgment involving right and wrong will encourage the child to think. It may take a while for the child to understand that he may answer something that might be different from what you are thinking. And for the first few times, I wouldn't say what I thought, as the teacher. Get the child used to the idea that it is good to have his own analytical thoughts and that you are interested in what and how he is thinking.
Teaching with the Take a Stand! series helps me get to know my children and students better and it helps them how to think critically, form historical judgement, and express themselves in speech and in writing.