"The Disposables of the Victorian Society: The Darwinian Critique of Social Treatment of Children in Victorian Era". This can be a very good thesis statement which will give you the possibility to dwell on a number of issues of the Victorian society with Oliver Twist as the point of departure and reference.
To defend a statement you need engage with the social criticism of the Victorian age particularly the dualism of morality, the emergence of the bourgeoisie class in the industrial and their influence in the post industrial society, prostitution and the concept of the fallen woman in the Victorian society. You can consult Henry Meyhew's "London Labour and London Poor". It will be of great help. As the theoretical orientation of the thesis will be Darwinian you have to be well acquainted with the primary Darwinian theory of "Natural Selection, Sexual Selection" and also the writings of Herbert Spencer who advocated Darwinian principles amidst severe criticism against Darwin. Apart from that the works of Malthus, Galton will come handy to grasp the notion of social Darwinism and the theory of the elimination of the weak for the proper development of the society. Donot forget to consult the works of Gillian Beer particularly Darwin's Plots.