Early in the chapter, Jem reveals to Scout why he was so shaken by finding his pants crudely mended at the end ch. 6 this: "'Like somebody was readin' my mind . . . like somebody could tell what I was gonna do. Can't anybody tell what I'm gonna do lest they know me, can they, Scout'" (58)? Jem is realizing that while they have been trying to sneak peaks at Boo, he really has been watching them all the time.
This interaction continues in ch. 7 with Jem and Scout finding presents in the tree. Jem and Scout discuss what to do with their findings. Jem asserts that they should write a letter and leave it in the tree to thank whoever is leaving the presents. Then he recalls that a similar plan was how he lost his pants in the previous chapter. He seems to realize this and stops the idea immediately, which only confuses Scout. This passage shows us that Jem realizes it is Boo leaving the gifts. Scout observes, "He had been on the verge of telling me something all evening; his face would brighten and then he would lean toward me, then he would change his mind" (61). Jem seems to want to tell Scout that it is most likely Boo leaving the presents.
Jem's suspicions are confirmed when Mr. Radley seals the hole with cement. Jem ends the chapter much like the previous one, alone and in tears. It is clear that he realizes Mr. Radley is trying to put an end to the innocent communication between the kids and Boo.