Nothing inspires dressing up by kids quite like the sound of "The Nutcracker Suite." The ballet's annual visit is a good time for the debut of a party dress since the chances to spill or roughhouse are limited.

The best clothes are the classics, those that can be worn without the hazard of style changes, plus easy fitting styles or sportswear parts that accommodate the changing size of children. More important this year are the warm clothes, helpful in households where thermostats are kept lower. CAPTION: Illustration; The ultimate party dress: all cotton velvet skirt with lace-trimmed cotton blouse and plaid cummerbund. By Beautique. Woodward & Lothrop, sizes 7-14, $48.

Royal blue velvet topped off with an ecru lace collar. Li'l Filly Originals, Inc. From Just So Children's Boutique, infant through toddlers, $54-$60 depending on size.

The perfect coat and hat for going to Grandma's house. An acrylic and wool blend plaid coat with velvet collar and matching hat by Rothschild. Sizes 2T-4T with matching hat and leggings $82; sizes 4-6X with hat $71.50; sizes 7-12 $75. The Esther Shop.

Brother and sister outfits in eggplant-color cotton velvet. Girls lace-trimmed dress $46, boy's shirt and romper $46, both in sizes 2T-4T. I. Magnin.

Warm as well as perfect for a holiday party, a Viyella plaid smocked dress. Sizes 2T-4T $45, sizes 3-6X $50. From Grasshopper, Inc. By Bobbi Tull.