The FDA is not convinced that BPA (the chemical bisphenol A used in plastics and resins) is harmful to humans, but after pressure from the American Chemistry Council, the agency has formally banned its use in baby bottles and training/sippy cups.
In practice, most manufacturers and retailers of children's goods have voluntarily not used BPA for the past several years to allay parents' fears or concerns so the FDA's ban is mostly a formality.
As recently as March the FDA said it was still evaluating whether BPA had negative effects on humans. Their researchers found that: "Exposure to BPA in human infants is from 84 to 92 percent less than previously estimated." And, "BPA is rapidly metabolized and eliminated through feces and urine...The center's toxicology research has not found evidence of BPA toxicity at low doses in rodent studies, including doses that are still above human exposure levels."
• FDA Bans Chemical BPA From Sippy Cups and Baby Bottles, NPR
• F.D.A. Makes It Official: BPA Can't Be Used in Baby Bottles and Cups, New York Times
• FDA Continues To Study BPA (March 2012), FDA