Originally Posted by
LapLap
Having had a chance to think about this, I'd recommend a visit to Hakone using the Hakone free pass.
You'll have the opportunity to cover a lot of ground and see lots of the landscape and because you use a whole variety of transportation - rail, cable cars, ropeways, boats and only at the end a bus, you don't have to cover a lot of distance on foot, which I know will quickly get tiring for a 5 year old, and for both of you in August. Although the area in itself should give you a bit of a respite compared to the heat sink that is Tokyo.
More info here
http://www.odakyu.jp/english/freepass/hakone_01.html
Not sure I would really recommend Hakone for a six night trip with a five year old in tow as a day trip, mainly because of so much time on transportation and so many changes of transportation modes involved. If your daughter has a lot of stamina and really enjoys travelling though, there are indeed lots of fun things to do.
If she likes swimming, Yunessun could another option in Hakone.
http://www.yunessun.com/english/yunessun.html