Golden Gate Park

Golden Gate Park used to be a vast wasteland of sand chilled by forceful ocean winds, until in the 1870s a brave Scotsman, John McLaren, had a vision to turn it into a park where future San Franciscans could escape the crowds. He planted over a million trees and acres upon acres of grass, flowers, and plants, and the result is gorgeous Golden Gate Park! When McLaren agreed to be superintendent of the park, he said: "There will be no 'Keep off the Grass' signs."

There are many areas to 1,000-acre Golden Gate Park, including some museums and attractions- here are a few tips:
You can't walk into Golden Gate Park from anywhere you want along its borders, because it is fenced off, even to pedestrians. You have to enter by foot or car from 7th, 9th, or 19th Avenue in the south. From the north, enter via 8th Avenue.
Golden Gate Park is so big that you may want to rent bikes at Stow Lake to get around. You can also drive around- while the crowded area around 19th Avenue is usually backed up, the meadows area on Kennedy Drive in the west of the park is nicer, and there's plenty of parking along the street.
PLAYGROUNDS
I love the playground called Mother's Playground (pictured above), located on Martin Luther King Jr Drive, near Crossover Dr (which is a continuation of 19th Avenue). The playground is at the bottom of a huge bowl-shaped sloped lawn. Kids can run up and down, and roll around on the grass to their heart's content. It's a happy scene here, with tons of kids playing frisbee with their parents. It's a great place to have a picnic or take a nap at the top of the hill in the sun after a busy day in San Fran. The trees around it are truly glorious. There are restrooms here.
There is a great newly-renovated playground and 1912 antique carousel at Kezar Drive, open during the summer and on weekends.
Boat Playground is at 45th Avenue and Lincoln Way, and is a lot of fun for kids! A large painted boat- like a huge canoe- sits in the sand, and kids can climb in. There is a green play structure, and there are cypress trees all around- very pretty!
Or try the expansive blue play structure at 10th Avenue and Fulton. It is loads of fun and is surrounded by a large grassy lawn.
There is a playground on Bowling Green Drive, with lovely sand areas, tires, and a wooden play structure. It is surrounded by gorgeous trees.
LAKES
It's pleasant to sit beside Stow Lake, which is situated in the middle of the park, and feed the ducks, or rent a paddle boat and coast along the water. It's very peaceful here.
On weekends, model boat enthusiasts sail their miniature boats on Spreckels Lake, and kids like to watch! This is located along Kennedy Drive opposite 36th Avenue. There's plenty of parking along the road here.
GARDENS AND MEADOWS
By far the loveliest area to me are the meadows on the west side of the park along Kennedy Drive. If you enter from the north on 8th Avenue and drive along Kennedy Drive, you'll avoid all the mad traffic around the middle of the park, and you can zoom right into a parking spot along the road and be having your picnic within minutes. There are lovely secluded spots among the hilly daisy-covered meadows.
If you follow Kennedy Drive all the way to the ocean, you will find the Dutch Windmill, set in a lovely field of poppies or tulips (depending on the season). It's so lush and green here, and there is an abundance of thick Monterey cypress trees.
More towards the middle of the park, best accessed by foot from the south via 9th Avenue, San Francisco Botanical Garden is nice for a walk. Kids like to run around on the hilly lawns, and feed the ducks in the pond. The Japanese moon garden has a wooden platform to walk out on, and look down at the water below. The maple trees there are lovely. There are some extremely rare and unusual trees, such as one from Lord Howe Island in Australia. Other than that, the gardens within the arboretum can be quite dry and plain.
MUSEUMS
California Academy of the Sciences is a large aquarium in the center of the park, near 9th Ave. It has an incredible Amazon exhibit with three levels showing little frogs, large fish, vines, and live butterflies from the Amazon. It is worth the large entrance fee. 
There is also the De Young Museum, an art gallery in a copper avant-garde building with a 360-degree view from the observatory.
DOGS
Dogs are allowed on-leash in Golden Gate Park. There's a good off-leash area on the east end of the park bounded by 2nd Avenue, Lincoln Way, 7th Avenue, and Martin Luther King Jr Drive.
BEACH, AND FOOD
On the far west end of the park, you can walk across the Great Highway to Ocean Beach! Here, there are plenty of happy people taking a stroll along the boardwalk. The beach is expansive, flat, and wild, with cold ocean winds. Dogs are allowed off-leash from Stairwell 1 on the far northern end to Stairwell 21 near Beach Chalet.
Across the street, check out the historic Beach Chalet. Inside it's lobby, you can see the historic murals and read about the building's interesting history. There are some really cool exhibits, like the miniature model of Golden Gate Park. If you're hungry, there's a casual brewery-style restaurant upstairs with ocean views, but the ceiling is so low and it's so loud inside that you don't feel relaxed or happy about the views. Plus, the food isn't that great. The wait for a table is only 15 minutes here (because the diners can't wait to get out of the noise!), but I suggest coming early and waiting longer for the better Park Chalet Coastal Beer Garden next door. The wait for a table can be up to an hour, but once seated, you'll have a lovely spot on the lawn in the sun and your kids can tumble around on the little hilly areas.
It may be easier to eat at the Inner Sunset District Neighborhood if you're nearer Stow Lake, Strybing Arboretum, and the middle of the park. There are some far superior restaurants there and it's a short walk along Martin Luther King Drive to 9th Avenue.

Directions

You can take the MUNI light rail to get here. From Powell station, take the N (Judah) line towards Ocean Beach. Get off at Judah and 19th and walk north along 19th Avenue into the park. You'll be near Mother's Playground and Stow Lake once you enter the park.
You can enter the park very easily by car from the north. After passing over the Golden Gate Bridge, follow the signs to the park. You will enter on 8th Avenue. From there, if you turn west on Kennedy Drive, you will come to Spreckels Lake and some wonderful secluded meadow areas, and finally, to the Dutch Windmill, Beach Chalet, and the beach.
For parking, the Music Concourse Garage is open 7am-7pm every day, and costs $5 an hour or $6 an hour on weekends. The entrance is at 10th Avenue and Fulton Street. I find it easier to use the time-limited parking along the streets within the park.
San Francisco Botanical Garden is located at 1199 9th Ave, San Francisco CA 94122. Open daily at 7:30am and closes around 4-6pm depending on the season. $9 for adults, $6 for teens and seniors, $2 for children, and free for kids 4 and under.
Beach Chalet, 1000 Great Hwy, call (415) 386-8439. They have parking (which is probably full), or you can park along Kennedy Drive. There is sometimes parking along the ocean between Fulton Street and Lincoln Way.

Click on map for interactive view