A federal court in Denver on Thursday approved a landmark $65.5 million settlement for young child-care providers, the culmination of a four-year fight to compensate 100,000 au pairs around the country for years of low pay and substandard working conditions. As a result of the settlement, au pairs will be free to bargain for fair-market wages and must be informed of their rights to negotiate by the sponsor agencies, Eddie Evans, a spokesman for the Boies Schiller Flexner law firm that represented the au pairs, said in a statement. The lawsuit, filed in 2014 by a dozen former au pairs from around the world, claimed the 15 companies that bring workers to the United States colluded to keep their pay below minimum wage and lied about the au pairs’ ability to negotiate higher pay.