Task: Question Answering
Input (English): Passage: During their summer vacation with their grandfather Mori, Rocky, Colt and Tum-Tum take a test on an obstacle course in pitch blackness. They passed the test. Later that night, he overhears Rocky and Colt planning on not returning the next year, due to getting older and he becomes depressed at this.
Returning home, Tum-Tum is also becomes very depressed that his favorite TV Series Dave Dragon is going off the air soon and not even food can cheer him up, which confuses his mother Jessica. They meet a new neighbor, Amanda who accidentally sends her remote controlled helicopter into their house; she apologizes, and Jessica invites her to attend Tum-Tum's birthday party at Mega Mountain; an amusement park modeled after Six Flags. Once they get to the park, Rocky goes off on his own to be with his girlfriend Jennifer while Tum-Tum convinces Colt to go with him to a special live Dave Dragon show as his last performance. While the kids are enjoying themselves, a criminal named Mary Ann "Medusa" Rogers and her men sneak in and commandeer the park, disabling many rides and shutting the place down to hold the patrons hostage in exchange for $10 Million from the park's owner Harry Jacobson. The boys and Amanda discover this and save Dave from being captured, as he seems to be the only viable threat to Medusa's plans. Amanda uses her laptop to try and override the controls, but Medusa's henchmen wrest control from her. Fearing they will interfere with her, she sends her idiot nephews out to capture them, but they are tricked by the boys and their access to an arsenal of small weapons and devices that Amanda possesses. Meanwhile, Dave sneaks into the command center, but is quickly discovered and captured. 
Question: Who overhears a conversation about planning on not returning to summer vacation next year?
Output (English): Tum-Tum.