There are many places in the novel that show that Tom was an innocent and kind man. For one thing, during the court examination, it comes to light that Tom would help Mayella with chores without pay. He helped her out of his fondness for her. Here is the dialogue:
"You're a mighty good fellow, it seems—did all this for not one penny?" "Yes, suh. I felt right sorry for her, she seemed to try more'n the rest of 'em-" "You felt sorry for her, you felt sorry for her?" Mr. Gilmer seemed ready to rise to the ceiling. The witness realized his mistake and shifted uncomfortably in the chair. But the damage was done. Below us, nobody liked Tom Robinson's answer. Mr. Gilmer paused a long time to let it sink in. (19.124-127)
You can also point out that Tom was handicapped. His crippled left arm made it clear that he could not have hit Mayella. Only someone with two strong arms could have done that, namely, Mr. Ewell, Mayella's father.
Another point is that Mr. Link Deas, his boss, vouched for him. By all accounts, Tom was a very good man. Tom's pastor, Reverent Sykes, also vouched that Tom was an outstanding man. He also sought to raise money for Tom and his family, which get us to the point of his children.
When Scout and Jem went to church with Calpurina, they heard Reverend Sykes. During the announcement time, the church was seeking to raise money for Tom and his family. He says that Tom's wife, Helen, has three children. Here is the quote from chapter 12:
To Kill A Mockingbird
My curiosity burst: “Why were you all takin‘ up collection for Tom Robinson’s wife?”
“Didn’t you hear why?” asked Reverend Sykes. “Helen’s got three little’uns and she can’t go out to work—”
It is clear that Tom is a mockingbird. He harms no one and does good to all. To kill him is to harm something beautiful for no reason at all.
In the book,To kill A Mockingbird by harper Lee, Tom is much like a Mockingbird because he tries to help Mayella Ewell "bust up a chifforobe", fix her screen door, and retrieve a box from on top of a chifforobe.
The Mockingbird of the proverb is an innocent, harmless creature which does it's best to please it's hearers by singing (Tom tries to help Mayella Ewell and other white people when ever he can), but is defenseless against hunters (Tom is African American and at that time Tom is belittled for that and is not granted any sympathy or power).
In the novel, the wrongness of killing the bird is clear, but it becomes a metaphor for the wrongness of harming innocent, vulnerable people.
In addition, Tom Robinson is a disabled man. One of his arms is 12 inches shorter than the other. Check out page 255 for a quote.
"Tom Robinson was probably the only person who was ever decent to her."
This shows that Tom was very caring towards Mayella.
"Mr. Finch, I tried. I tried to 'thout bein' ugly to her. I didn't wanta be ugly, I didn't wanta push her or nothin'."
This shows that Tom meant no harm towards Mayella.
"Sam [one of the Robinson children] was trotting behind his mother when they came up. Dill said Helen said, 'evenin’, Mr. Finch, won’t you have a seat?' But she didn’t say any more. Neither did Atticus. 'Scout, said Dill, she just fell down in the dirt. Just fell down in the dirt, like a giant with a big foot just came along and stepped on her. Just ump—' Dill’s fat foot hit the ground. 'Like you’d step on an ant.' Dill said Calpurnia and Atticus lifted Helen to her feet and half carried, half walked her to the cabin. They stayed inside a long time, and Atticus came out alone. When they drove back by the dump, some of the Ewells hollered at them, but Dill didn’t catch what they said."
This shows that Tom had family.