I took along my two boys (10 and 7 years), they both reckoned it was awesome and I have to agree with them. They tried out almost every bike available, had a go at bike polo, tried the virtual velodrome and scalextric, checked out everything at all of the festival parks along the route, and thoroughly enjoyed cruising round the route with the thousands of other folk who turned up.
Apparently the numbers were estimated at 70,000, and from everything I saw it was a great success. The boys are insisting we go again next year...