In Hugo's depiction of a world where human rights are not even close to be recognized, the presence of children help to enhance this idea. When we consider the most innocent of society, children have to rise to the top of this list. A society that mistreats its children is one that is begging to be criticized and reformed. In the end, Hugo seeks to bring out the idea that society is misguided and misdirected in its ends. Justice is for sale and human dignity is not something that is valued. In his inclusion of children in this world, Hugo is able to vividly display this theme in the most broad of ways. We might criticize the actions of Valjean and even Fantine. Yet, when we see children, such as Fantine's, left to their own devices, denied their opportunity to live a productive life and victim to the practical and institutional unfairness in the world, it helps to bring to light the need for social change. The presence of children helps to also bring to light the idea that what is can be transformed into what can be, as there exists such hope in the children who can be the inheitors of this new design.
In a novel that illustrates the way the deck is stacked against the working classes of France—starting with the harsh jail sentence Valjean receives for stealing a loaf of bread to help feed his sister's starving family—children function as symbols of the innocent and good who are forced to suffer in an inhumane social order. The novel was published in 1862, the height of the Victorian era, an era in which readers liked to see children depicted as innocents who could touch adult hearts (think of Tiny Tim in A Christmas Carol and Little Eva in Uncle Tom's Cabin, both wildly popular works.)
In the household of the unspeakable Thénardiers, Cosette is exploited and forced to spend her childhood as a servant, even though money has been provided for her support. The Thénardiers also kick Gavroche, their oldest son, out of the house when he is young. He becomes a street urchin. Eponine, the Thénardiers daughter, a good and noble person, is pathetic and misused. None of them have what we would call a "real childhood." All of these characters hold onto their goodness and generosity despite how they have suffered, reflecting the Romantic notion that children are born innately compassionate, generous, and willing to sacrifice themselves until society warps them and makes them hard.