This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / The Mysterious Benedict Society
Milligan recalling how he got his memories back to Reynie, Sticky, Constance, and Kate, "in a voice so happy he almost sang". This is a huge contrast to when Milligan told the story of what he remembered ten years ago, without a trace of excitement in his voice. He says that regaining his memories was the best moment in his life.
Kate trying to hold back her tears and failing when Milligan is talking about getting his memories back. The ferocity in her voice surprised her when she forbid him from going on a hopeless mission that she would have lost him to. She asks how he can possibly leave her again, showing how badly her 'abandonment' affected her despite denying it did through the whole book. Milligan looks like he was slapped in the face as tears brimmed his eyes, saying it was the last thing he wanted to do. He even tells her that he loves her a little later in the conversation.
When Sticky is reunited with his parents, after an emotional conversation with Mr. Benedict about how his parents didn't think they were better off without Sticky, like Sticky though they did, but thought that Sticky was better off without them. They became poor, using all of the money won from the game shows they made Sticky participate in to finance searches to find him. They did all of this before Mr. Curtain's Whisperer plans were thwarted, meaning that even with the influence of the Messages they looked for their son because they loved him.
In the second book, when McCracken walks into the cave, implying that Milligan was killed, caused Kate to burst into tears. Mr. Benedict, in an attempt to comfort, falls asleep to due the sadness of the situation triggering his narcolepsy, which shows how upset he was and how it affected him.