In 2007 there was a scare related to the presence of lead-containing paint on Chinese toys. This resulted in several restrictions on Chinese toy imports imposed by many countries, the U.S. included. China responded by reducing the lead content to acceptable levels, and the restrictions have been largely lifted.
You mention a yo-yo toy. This is a good choice since it has no small, painted parts that a child might break off and ingest. And playing cards would pose no risk or restrictions whatsoever.
So long as the goods have paper work that is in order (see links to U.S. Customs service and check with any of a large number of Chinese export companies for requirements), your yo-yos should be importable without restriction.
There is one possible snag, however, and this is explained in the reference. It involves a new procedure introduced in June 2010 of inspection at the port of entry by the Consumer Product Safety Commission (CPSC). They use portable X-ray Fluorescence scanners (XRF) to measure lead levels. So long as your toys pass inspection, there should be no problem.