Kugenuma Kaigan -- great spot with its paddling pool fountain, playground and beach with nice view of enoshima... http://en.wikipedia.org/wiki/Kugenuma_Station
we even camp there some saturday evenings in a field by the  beach
there's a bakery by the station to buy a picnic lunch at

From Shibuya take the express to Fujiasawa, then step across the same platform to take the local train a few stops to JR Kugenuma Kaigan Station

Inokashira Park Zoo is a nice mix of a big free entry park with boating lakes, small playgrounds, woods / nice cherry blossom viewing etc in Spring, river with grassy banks to picnic on, and a small zoo with elephants, monkeys, cheap fun amusement park, playground etc in two parts separated by a bridge over a road. For a leisurely walk and full day of activities, enter via Inokashira Koen station, and finish up going back by Kichijoji station.

Inokashira Park Zoo is…

jacuzzi, slide, big kids pool....
lovely warm water

only a few hundred yen per hour
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• Hakuba (Nagano)  -- Snow Tour (March) Tobogganing and nursery slope skiing, snowmen and hanging out at the Lodge. For kids aged 3 years and upwards… -- Mountain Bike Event (August) 
• Yoyogi Park (Harajuku)
• Kugenuma Kaigan (Shonan Beach with pool & park)
• Odaiba Outdoor Pool (Odaiba)
• Okutama Mountains, River, Onsen (Okutama 1 hr from Shinjuku)
• Shikine Island (Ferry from Hamamatsucho Takeshiba)

 
•Joban Hawaiians (Huge waterpark & onsen Ibaragi)
•Jidokan (Kids indoor playground, Shibuya)
•Kodomo-no-shiro (Omote Sando, Kid’s Castle)
•Puro Puro Land (Hello Kitty etc, Tama Center)
•EdoMonogatari Onsen (Odaiba)
•Odaiba Sports Center (Pool / jaccuzi, Odaiba)
•Shinagawa Aquarium (Shinagawa Seaside)

Most Saturdays after her playgroup, Cissie and I visit Shibuya Sports Center from about 6:45pm.  Its located near Hatagaya station see notes, but we cycle there from Shibuya (passing nearby Yoyogi park.)  We'll play in the kids room on 2F which has slides, climbing, balancing and trampolines for a while then get in the kids pool (60cm) for the last hour until 9pm. After that we're up for some dinner somewhere and heading home...

Shibuya Sports CenterFeaturing…

The main attraction in Tama is Sanrio Puroland , a theme park dedicated to Hello Kitty and her cute clones.

This little Disney-like indoor amusement park features a nice little ride around it on a waterboat through cute Hello Kitty character populated landscapes, some nice shows featuring acrobats, singing, dancing acting, 3D cinema etc and a great evening show. Great for younger kids

To get to Puroland you walk up the hill from Tama Central station and…

Shikinejima island is my favorite spot in Japan, which we've visited dozens of times. There is a free campsite in a sandy bay during GW and summer, and a smaller free grassy one to use near the village at other times. There are several free rotenburo (hot springs in sea), lots of walks in the hills and woods, dozens of pristine beaches with clear water and semitropical fish, and great views of the other islands etc.

It's possible to takyubin (parcel delivery)…

Spa Resort HAWAIIANS is a wonderful place for a family visit in any season, but particularly great during late autumn thru spring to be spending warm days (and nights) in swimwear in the various themed indoor pools and onsen style outdoor pools that you can swim around in whilst…

Kodomo no Shiro between Shibuya/Omotesando stations is a great place to spend a day whether its rainy or sunny. It has an indoor swimming pool that's always empty, outdoor (over 3 yrs old) and indoor adventure playground, wall-painting/crafts room, live music room, changing interactive exhibitions (such as optical illusions, train sets, model making etc) pool on the roof in summer...etc.

COST:

General Admission:  Adults (Age 18 and over) 500yen, Children (Age…