The major US toy manufacturer that suffered a breakdown in supply chain from China on account of legally unacceptable toxic substances in its products is

Mattel, Inc. faced a major supply chain crisis in 2007 when millions of toys manufactured in China were recalled due to excessive lead content in paint and other toxic substances. This affected iconic brands like Barbie and Fisher-Price. The company incurred heavy losses and had to overhaul its quality control systems. The other options are not major US toy manufacturers.