Mattel Inc., Los Angeles, plans to sell its Learning Co. division. The burdensome software unit, acquired last May for $3.6 billion, has been a money loser that led to ballooning debt and the resignation of CEO Jill E. Barad in February. Mattel has retained investment firm Credit Suisse First Boston Corp. to find a buyer for the division, purchased to move forward Mattel’s effort to tap the growing market for interactive toys. The Learning Co. was to immediately add $50 million annually to Mattel’s bottom line, but instead added losses of $206 million. Industry experts said it would be difficult for Mattel to “get but a fraction of what they paid” for The Learning Co., the report said.