I do not want to do this assignment for you, but I would be happy to give you some pointers and direction!
First, consider WHY Boo Radley saved Scout and Jem. Jem and Dill showed an interest in Boo Radley. Of course, at first, it was based upon the idea that he was a deranged and dangerous person, but later they started to see him as a person. Boo would have appreciated this interest, even from children. In fact, he showed his appreciation by leaving toys in the tree until his father filled it in.
Next, let's consider WHO Boo Radley is. We know his is kept shut in his home because he does not "fit" in proper society. We know his father seems to have some embarrassment for him. In addition, it is likely that his father spoke of the trial in town, with Atticus defending Tom Robinson. He would maybe identify with Tom in that they are both outcasts and underdogs. People are embarrassed and frightened of them. He would appreciate that Atticus was defending Tom even though it was not the socially acceptable thing to do.
With this analysis, you can see that Boo would have appreciated the children for their interest in him and would have appreciated their father for taking a stand for the underdog.
Remember to write in the first person (using pronouns like I, we, me, my) when you write your dialogue.