This book is a great concept, and I have taken a few ideas from it, not least the 15 minutes outside a day, and my four children and I have had some fun times outside using it.
However, as it is written by an American for her own country, I must say that it is rather weather dependent. The author clearly lives in a country where at least 4 months of the year are roasting hot, so that water fights and similar water games are viable activities, and also where there are a few months of plenty of snow. This means that of the ideas presented, many if not most of them are rarely useable. Of the rest, some of them are culture specific and use amenities that may easily not be available to us city-dwellers or even those in the country!
So yes the concept is good and I have got some good ideas from it, but overall I don't think there were enough useable ideas for the British market and I would not recommend this as a good buy here.