Page Six learned that Rosengart sent the Daily Mail a legal letter on Sunday — which we reviewed — in which he demands an internal investigation take place concerning the exploitation of using Spears’ minor children, Sean Preston, 17, and Jayden, 16, whom she shares with ex Kevin Federline. “The Daily Mail, through Daphne Barak, posted a story yesterday containing numerous false and defamatory fabrications concerning my client Britney Spears that are attributed to Kevin Federline and his children,