Your family’s calendar is already filling up with holiday parties…time to start shopping for cute kiddie clothes. Starting this Sunday, both NYC Firefly boutiques are hosting sales, offering 20% off select holiday dresses and formal wear. Even if you’ve got clothes to last through Christmas 2010, we suggest popping in, as large toy sets will also be discounted. 224 Front St between Beekman St and Peck Slip, 646-416-6560; 240 Seventh Ave between 4th and 5th Sts, Park Slope, 718-965-3535, fireflychildrensboutique.com.

It looks like the folks at Racked, one of our favorite shopping websites, had it right when they said “this year’s holiday season might go down in history as the December of the pop-up shop.” We recently learned Jade’s Toybox and Zaba, two children’s online retailers, have opened up a temporary brick-and-mortar store in Tribeca through Christmas Eve. In addition to selling unique clothing and eco-friendly toys from the two companies, the shop will host a slew of family activities. Kids can make holiday crafts out of recycled materials, write a letter to Santa and get their picture taken with a 20″ x 24″ Polaroid camera. Parents can also get in on the action: Esther K. Smith, author of How to Make Books and Magic Books and Paper Toys, will lead workshops on how to make pop-up holiday cards and ornaments. 25 North Moore St at Varick St (917-349-5107).

Evidenced by our many, many blog posts on sales this week, holiday shopping is in full force. At the Goddard Riverside Community Book Fair this weekend, you can strike a seasonal balance between mass consumption and giving. Sponsored by the local publishing industry for over 20 years, the sale benefits the namesake community center. Shoppers can choose from thousands of brand-new donated tomes (including lots of children’s books), which are sold at half the normal cost. For the best deals, go on Sunday, when prices will be slashed down even more. Sat Nov, 21 10am–6pm, Sun Nov 22 11am–5pm. Goddard Riverside Community Center, 593 Columbus Ave at 88th St (212-873-6600, goddard.org).

Dressing your little ones in cute, stylish clothing without breaking the bank can be a challenge—especially in this city. That’s why, this past spring, we presented a guide to the best children’s discount stores, consignment and resale shops, thrift spots and retails chains around the city. We’re so happy to report that Shop Lucky Finds, one of the kids’ resale shopping events we highlighted, is hosting an event this Saturday, November 21 from noon to 4pm at St. Jean Baptiste Community Center on the Upper East Side. Stock up on used clothing, toys and gear from companies such as Jacadi, Catamini, Petit Bateau, Baby Bjorn and Skip Hop at super-low prices. In addition, nine vendors will set up shop to sell their new goods at sample sale prices. Keep an eye out for gloves by Bear Hands, clothing from Pink Chicken, belts from Rockin Robin and headbands from Mikayla’s Creations. Bonus for those with babies: strollers are welcome!

Get ready to add one more stop to your annual winter visit to Rockefeller Center. Lionel Trains has opened up a pop-up store at 30 Rock for the holiday season—the first retail shop in the company’s 109-year history. The 1,100-square-foot-space boasts fully operational train displays, a Christmas tree and hundreds of Lionel’s popular items for sale (we can’t wait to check out the Beatles Box Car and the Wizard of Oz Box Car). Plus, new this year: a train set made especially for toddlers for just $50.

Head to chic boutique Estella this Thursday, November 19, where SHirin Kids, best known for its line of artsy hand-screened tees, will show off its foray into dresses. Act now: The frocks are limited-edition. Fans of the eco-friendly line can also peruse the “Winter Wonderland” collection, which includes SHirin’s signature tops and onesies. Bonus: If you’re one of the first 50 shoppers, you’ll snag a free SHirin tote bag.

For more savings, return to Estella next month: From December 3 through the 24, the store will have its annual holiday sale, during which you can stock up on cute kiddie clothes for up to 50% off.

Why wait until spring to clean out your closets? This Saturday, Score! is hosting one of its pop-up swaps, where you can exchange your tired wares for new-to-you goods. Although not specifically aimed at families, there should be plenty of kids stuff: Score!’s received so many children’s items (clothes, DVDs, books, toys) in the past, there’s now a “Kiddie Corner.” And since it’s the season for giving, the $3 per person entry fee (kids under 11 are a suggested donation) will benefit City Harvest, and any leftover items will be distributed to nonprofits around the city. Sat, Nov 21 1-7pm. 3^rd Ward, 195 Morgan Ave at Stagg St, Brooklyn. RSVP at scoredatscore.com.