Harry Potter's mistreatment by his Muggle family does not amount to a legal wrong. Notice that Dumbledore did not threaten the Dursleys with legal proceedings, either in Muggle or Wizard tribunals. The ethic of equitable treatment is societal and lacks a legal basis in Anglo-American family law. Family law has many facets; it is an amalgam of legal rules and principles. My focus is the lens of property law -- in particular, family property norms -- although it is also plain that the Dursleys have not violated non-property based family law norms.
James C. Smith,
Harry Potter & the Law: Family Life and Moral Character
Available at: https://digitalcommons.law.uga.edu/fac_artchop/568