Today's guest blogger is Missy W. from Gearhead Mom, a site that reviews kids' toys and gear. Here are five of her favorite free things to do with kids in the San Francisco area:

Crissy Field: Sitting at the edge of The Presidio, Crissy Field began as a marsh and seasonal home of Ohlone Indians, and later hosted Spanish and Mexican ships, a Grand Prix raceway, an historic army airfield, and a Coast Guard station. Today, the shoreline provides both indoor and outdoor amenities, including a well-groomed promenade trail, beaches, picnic tables, tidal marsh overlooks, and a renowned windsurfing site, as well as cafés, bookstores, and an environmental education center. Our 3-year-old daughter can spend hours watching the windsurfers, run along the sand amidst all the local dogs, or roll down the hill at the mini amphitheatre near the Warming Hut. It’s always chilly and windy here, so pack layers. Free parking is a piece of cake, right behind the Warming Hut. You can walk along the pier and watch people fishing before picnicking along the shore. The recent renovation of Crissy Field is beautiful. It’s a showstopper, all that nature.

Sea Lions at Pier 39:  When we have visitors, Pier 39 is the bane of my existence. It’s hokey, it’s cheesy, it has a fake earthquake zone. But it also has one of the coolest free attractions in town: hundreds and hundreds of loud, barky, pushy sea lions. After the Loma Prieta earthquake of 1989,  the sea lions migrated from their previous home at Seal Rock to the docks at Pier 39. Lucky us! You can stand mere feet from them and watch as they fight for primo space on the docks, sun themselves, or take a dip. Man, they are loud. Staff from the Marine Mammal Center’s kiosk, located next to the sea lions, are happy to inform visitors about the animals. Each weekend, weather permitting, the center provides volunteer docents at K-Dock who explain sea lion behaviors and answer visitors’ questions. As frightening a tourist trap as it is, Pier 39 is one of our favorite weekend destinations. Like Crissy Field, the weather can be mercurial. We always have a few sweatshirts tucked into the stroller. Parking is tough (and usually not free), but you can always park in neighboring North Beach and walk over if you are committed to a fully free outing.

Lombard Street: The other day we took Sy to Crissy Field and promised her we’d drive down the illustrious Lombard Street Hill, a.k.a. "the crookedest street in the world," on the way home. As we twisted and turned down the hill (at a heartstopping speed of 7 m.p.h.), Sy started squealing and shouting about how we were on our very own rollercoaster ride. The gauntlet had been thrown. My husband threw the car into third gear and told her she aint seen nothin’ yet. We took her on her very own roller coaster ride through the hills of Russian Hill and North Beach. I’ve never heard her yell with more excitement and we weren’t even speeding. I wouldn’t suggest this if you are new to San Francisco or driving a rented stick shift, but if you are even a decent hill driver, then buckle up and enjoy the ride. Of course, the price of gas is far from free, but the reaction of your kid will be priceless. Check out our rollercoaster hills route.

Koret Children's Quarter in Golden Gate Park: When friends with kids come to visit, this park, the oldest children's playground in the country, is one of my favorite places to show off. The carrousel has been in operation since 1888 and the hill slides will have you back for more.

Little Farm: Tilden Park in nearby Berkeley is a magical place. It has a steam train, an impossibly fast merry-go-round, many acres of parkland and picnic areas and even its own little farm called, conveniently enough, Little Farm. Built in 1955, it features a variety of farm animals including cows, sheep, goats, rabbits, chickens, and pigs. Several heritage breeds are preserved here, including Milking Shorthorn Cattle. Visitors are welcome to bring lettuce or celery (but nothing else) to feed the residents. The animals are well taken care of and the staff is happy to chat with you. Our little girl is a big fan of the cows. There are gorgeous trails and places to picnic within Tilden Park. You can definitely make a day of it.

More about kid-friendly San Francisco:
WeJustGotBack.com's Insider Guide to San Francisco
Travel Savvy Mom's Land of the Free: 5 fab freebies in San Francisco
Rookiemom.com's Land of the Free: 5 fab freebies in Berkeley
Jumping Monkeys' Land of the Free: 5 fab freebies in North Bay