Atticus has to go to Helen Robinson's house to deliver the bad news that Tom was shot and killed in a foiled and desperate escape attempt. He encounters Jem and Dill along the way and reluctantly takes them along. When Helen gets the news of her husband's death, she crumples, according to Dill, "...like a giant with a big foot just came along and stepped on her." The reason this scene is in the book is because the reader is seeing the story through the eyes of the narrator, Scout. Scout wasn't there and we need to know what happened, so Dill and Jem relate the events to Scout who relates them to us, the readers. Also, through this scene and Dill's description to Scout, we see the simplicity with which the Robinson's and the other black families live, and how they take care of each other. Lee wants us to see these are good people who do no harm to anyone. We also learn that the Ewells place has to be passed by on the way to the Robinson's place and that as Atticus, Jem, and Dill passed by, the Ewells yelled unkind words at them. This shows us again how bad the Ewells are, especially as compared to the Robinsons.
Atticus goes to Helen Robinson's home to tell her that Tom was shot and killed. On his way there, he finds Jem and Dill walking and decides to take them with him. When Helen learns that her husband was killed she falls apart. This scene is important to the story. Jem and Dill being present allows the reader to learn about it later when they tell Scout about it. Remember that Scout is the narrator in this story. It also serves as a reminder of how horrible the Ewell family is. As Jen, Dill, and Atticus pass by their home on the way to the Robinson house, they yell at them.
They went to Helen's house to tell her that her husband had been shot and killed and when this happens she breaks down crying. This is very important because this shows the boys maturation and understanding but they also understand how horrible and messed up the Ewell family who is the root of the whole problem as stated in the start of the book.