It took me quite a while, and only after discussing it with my math-smart husband, to figure out that for seven days in Venice we were better off buying the kids regular 7-day 65-euro passes just like our own than buying the 6-euro each Rolling Venice card and two 3-day passes (2 x 27 euro each kid) which is 60 euro for six days. Then, plus however many vaporetto rides on the 7th day for full price (9.5 euro) or 25 euro for the 24 hour pass.
I don't have a question, just sharing, but do please tell me if our calculations are not correct.
In addition to the cost, there are forms to fill out online for both the Rolling Venice card and the Unica card and ID's to show, so we plan to just buy passes at the train station as we always have before. Keeps life simple.
I should mention that the kids will be going to only two or three museums and churches, so no need for museum passes, or at least, not worth the extra trouble to get and then use passes. And not taking the ACTV bus from the airport. And my husband now has a painful arthritic ankle and we'll all be taking many more rides than we have before. So your own calculations about vaporetto passes for kids may differ.
I might have compared the cost-per-ride of regular passes vs the special kid passes sooner if I had searched this forum first (duh) and found the always-helpful acraven's answer to a vaporetto pass question from a year or so ago --- here it is:
The daily cost of a vaporetto pass drops significantly as the validity period increases.
One-day pass: 25 euros (2.6 rides per day)
Two-day pass: 35 euros (1.8 rides per day)
Three-day pass: 45 euros (1.6 rides per day)
Seven-day pass: 65 euros (1.0 rides per day)
(The pass-validity periods are actually in hours rather than days.)
The seven-day (168-hour) pass was a no-brainer for me on my recent nine-day trip, but it was frustrating that beyond seven days I was back to paying the higher cost of a shorter pass or buying individual tickets at 9.50 euros a pop.