EXCLUSIVE

Danica McKellar -- who played the beautiful Winnie Cooper on "The Wonder Years" -- has filed for divorce, TMZ has learned.

Danica filed the docs in L.A. County Superior Court against her composer husband Mike Verta -- citing "irreconcilable differences." The couple has a one-year-old son.

Danica and Mike were married on March 22nd 2009 in San Diego, and their first dance was to a song Mike wrote. The couple separated just last week.

Danica wants joint physical and legal custody of the son.

According to Danica, there IS a pre-nup which covers all the couple's property.