The kid in the Batman costume at the end is Dick Grayson
At the end of the film, a kid in a Batman costume, along with his parents, comes trick-or-treating to the Wayne Manor. Its entirely possible that this kid is none other than the future Robin, Dick Grayson, with his parents John and Mary Grayson. Considering that The Long Halloween's comic-book sequel is Dark Victory, which is a Robin origin story, this is a likely case of Futureshadowing. It would give Bruce an even more personal motivation to take Dick on as his ward and help avenge the murders of John and Mary Grayson if he recognizes the family as the first trick-or-treaters to visit his home in years.- Alternately, the kid is Batman Jones from the Silver Age comics.
The Maroni family was responsible for the Wayne murders in this continuity
Bruce implies as much when he mentions how his parents were the two innocent lives lost due to the Wayne-Falcone alliance. Its entirely possible that Luigi Maroni, or even Sal, organized the hit on the Wayne family in retaliation for Thomas saving Carmine Falcone's life, and later giving him legitimacy through the hospital project. It would also serve as a Mythology Gag to how, in the pre-Crisis comics, the Wayne murders were a Mob hit disguised as a mugging, which was the result of Thomas Wayne saving a Mob figure's (Lew Moxton's) life. the Joker attacked Harvey/Two-Face's Father, Christopher Dent
Alfred mentions that three families were attacked by the Joker on Christmas, and all of them were called Dent. In the comics, Harvey bought his father an apartment and occasionally visited him, so it's possible that one of the places Joker broke into was Harvey's father's place before Joker eventually broke into Harvey and Gilda's house.