Jem and Dill tell Scout that they are trying to peer into the Radley window because they want to send him a note. They want to be nice and ask him to come out so they can be friends.
Dill said, "We're askin' him real politely to come out sometimes, and tell us what he does in there- we said we wouldn't hurt him and we'd buy him an ice cream." (ch 5)
Throughout the book so far, the children have been trying to get Boo Radley to come out. At first it was just a game, and they thought of Boo as some kind of monster.
Jem gave a reasonable description of Boo: Boo was about six-and-a-half feet tall, judging from his tracks; he dined on raw squirrels and any cats he could catch, that's why his hands were bloodstained (ch 1)
By this point they have changed their attitude. They now see Boo as a human being. They want to write him a nice note. They want him to come out and play. They are not afraid. Of course they are still afraid. Atticus has told them to leave Boo and the Radleys alone, but they are not being obedient. They are too curious.
Jem uses a pole to try to deliver a message to Boo; this shows his bravery is limited. (enotes ch 5 summary)
The children are beginning to be more mature here, but they are basically still acting like kids.