Super tip: Check out Festivals.com for a pretty exhaustive listing of every festival in the country, with search capabilities by city.
Cheap trick: Ferry rides
Unlike the pricey city circle liners, commuter ferry rides are usually not that expensive. And to young children, heck, a boat ride's a boat ride. Climbing aboard to enjoy the view '- and the breeze '- is a great activity during the summer's hot and hazy days. If it's your first time out, bring Dramamine just in case.