A bit late I guess, but for next time, there's Manly Dam. During school holidays and weekends you would need to book a BBQ area, if you want a BBQ you might need to book anyway. Clontarf is a great spot, plenty for kids and a kiosk, but parking charges, same with Balmoral. I've seen Kinges amongst the boats at Clontarf,and often see a rise from the bus crossing the Spit bridge of the morning.