Central Theme: People can change. And if they can change, so can the world.
Compressed Adaptation: Even with 52 episodes to tell the story, this is still a children's adaptation and some parts are omitted because they're not appropriate - Fantine is never explicitly shown to be a prostitute, for example.
Cool Old Lady: Toussaint is far from young as well, and serves as something of a surrogate mother to Cosette.
Dead Person Conversation: Marius speaks to Enjolras' ghost when visiting the site of the Last Stand. Cosette tells him that sometimes she talks to her mother as well, showing that she doesn't think he's crazy.
Death by Adaptation: Fauchelevent dies of old age in the convent, shortly after which Valjean and Cosette take their leave.
Doomed Moral Victor: Les Amis, of course. Gavroche and Marius are the only ones to survive: Gavroche because he was saved by Chou Chou before the soldiers could kill him, Marius because Valjean saved him during the Last Stand.
Dramatic Irony: Fantine has no idea that Cosette is being abused and often says that the Thenardiers are taking very good care of her.
Establishing Character Moment: We first meet Gavroche as a baby. Cut to three years later and we see him put a mouse in Eponine's hair, when she's bullying Cosette. This establishes him as the kind of kid who will stand up for those who can't do so for themselves, and Foreshadows his joining Les Amis later.
Foreshadowing: When Gavroche and Cosette, as children, are running over a hill together, Gavroche falls and lies facedown for a moment. Cosette, concerned, turns around and says his name. When she finds him after he was shot at the barricade, he is lying facedown on the pavement. She gasps and says his name over and over, nearly in tears.
Karma Houdini: The Thenardiers subvert this. Monsieur Thenardier is arrested in one of the last episodes, and Madame Thenardier is stuck in same position Valjean used to be in, a paroled convict who has to show her papers to everyone. It's unlikely that she'll ever be living well again.
It's implied somewhat that Alain, the kid Valjean-as-Madeleine took under his wing and provided for the siblings of, was able to use his knowledge to prevent Montreuil Sur-Mer's economic decline by stepping in for them.