How does Jem feel about the items left in the tree in To Kill a Mockingbird?

Jem goes from being suspicious and curious about the tree gifts to being appreciative of Boo Radley's efforts.

When Jem first learns about the items left in the tree, he is skeptical.  The children have gotten used to the idea that the Radley place is dangerous and Boo Radley is a monster. Scout finds gum in the tree and eats it, but when Jem finds out he yells at her to spit it out. 

Jem stamped his foot. “Don’t you know you’re not supposed to even touch the trees over there? You’ll get killed if you do!”

“You touched the house once!”

“That was different! You go gargle—right now, you hear me?” (Ch. 4) 

The children do not know at first who has left the things in the tree or what they are there for.  They think that someone might be keeping things in the tree hollow.  It soon becomes clear that the items are gifts for them when they find two soap dolls that look eerily like Scout and Jem. 

Jem let me do the honors: I pulled out two small images carved in soap. One was the figure of a boy, the other wore a crude dress. Before I remembered that there was no such thing as hoo-dooing, I shrieked and threw them down. (Ch. 7) 

Jem is impressed by the soap dolls.  He and Scout discuss who might have made them, but it is becoming more and more apparent that the tree is on the Radley property and the only Radley they interact with (or try to interact with) is Boo.  When the tree hole is cemented by Nathan Radley, Jem is upset. 

The whole thing comes to a head the night of the fire.  Jem has figured it out by then.  He realizes that Boo Radley cares about them and is trying to reach out and make friends.  He sewed up Jem’s pants when he left them behind.  He put a blanket on Scout’s shoulders.  Jem tells Atticus that they can’t return the blanket because Boo will get in trouble. 

Like Scout, Jem is maturing.  When the story starts, Jem is still pretty young and looks at the world from a child’s point of view.  The development of his reaction to Boo Radley demonstrates that he is starting to mature.  He comes to understand that the presents in the tree are not dangerous, but are rather an attempt by a lonely, reclusive neighbor to make a friend.  Jem becomes protective of Boo.