It might be too cold to picnic at Ravinia Festival's "Winter Wonderland" event, but you won't have to pay for parking or a lawn ticket either. This is an off-season chance for families to cavort at the sublime summer hangout. No leaves, no party tents, no mobile shushing signs--just plenty of music. Choirs from five local schools will sing on the steps of the Martin Theatre while the Avalon Brass Quartet of Chicago, Midwest Young Artists' Chamber Music Ensemble, and Eileen Boever's Traveling Troupe perform in Bennett-Gordon Hall. Also on the grounds: Santa Claus, a magician, a storyteller, and Kohl museum craft projects, plus hayrides in the south parking lot. It's all yours, including free hot chocolate, with the donation of a nonperishable food item or two to be given to needy families in Moraine Township. Hours are 11 to 3, Saturday, December 2, at the park at Lake Cook and Green Bay Roads in Highland Park. Call 847-266-5100 for more information.