Playmates Holdings Ltd., which produces Teenage Mutant Ninja Turtle action figures and Disney princess dolls, said on Tuesday that its holiday orders from key retailers, including Wal-Mart and Toys R Us, are double what they were at this time last year.  The increase was attributed, in part, to the improving U.S. economy.  Major retailers, including Wal-Mart, have also reported a strong back-to-school selling season.