We are taking our 4 children (aged 6-12) to Venice July 17-19/08. I hadn't thought of planning any tours in advance until I started to read the forums. Should I book Doges' Palace tour? Do I need to book anything for St. Marks or can you just walk in? We're staying near St. Marks and arriving by water taxi. Should we take the trip to Murano? Any other suggestions? Thanks.