I'm new to the forum, but a long time fan of Rick Steves and his show. One thing he doesn't cover too much is traveling with children, so I'm sharing our itinerary for comment.
As an airline employee, we get to fly for free or insanely cheap, so that largely governs our travel dates. We plan on arriving this weekend, and departing the 19th as flights that day are very open, but after the 19th they are very full back to the US.
My kids are 10 and 8 and we have always done one large vacation per year and a number of smaller ones (road trips, camping, etc.) Italy is our big one this year and will be our first time to Europe! From previous vacations, we've learned we get to about 1/2 of what we plan because the kids determine our pace. Also, they tend to poop out around Day 10-12 away from home.
We are planning 5 nights in Rome. Staying in the Monti neighborhood to hopefully eliminate some walking, and utilizing public transport often to keep little legs rested as possible. Day 1 is going to be just recovery and adjusting to the "shock factor" one gets while visiting a new country. The only firm plan we have is the Vatican our final full day, as we already bought tickets online. The remaining days we "go with the flow" as the kids allow, but we are planning the major sites - Colosseum, Forum, Palatine Hill. If the kids still have energy the Capitoline Museums. Panthenon is a must, which can include Trevi and Spanish Steps, possibly incorporating one of RS walking tours. Also we are looking at the Appian Way to rent bicycles, which the kids would enjoy as a break from the constant art, and San Clemente is also likely. If we still have time, some of the nearby free churches or National Museum are toward the bottom of the list and it will depend on how we're doing up to this point. Instead of the typical American "go-go-go" attitude, we plan on taking our time and enjoying a slower European pace. So we see what we see.
Then off to Florence for four nights via rail which will be purchased the moment we get to Rome. (As nonrevvers it is never guaranteed we'll get anywhere so I try not to book too much nonrefundable things ahead of time. Usually works out okay!) Our hotel is immediately next to the Uffizi Gallery. One day will be a Pisa day trip. Otherwise, we'll cover the major sites from the Firenze Card: Accademia, Uffizi, Duomo. I think they will enjoy the Galilleo Science Museum as well, and I'd like to see the Boboli Gardens as I think the kids will enjoy it and it plays well with the Dan Brown novels for me. Again, as time allows (if there is any left) we'll cover the Medici Chapels or other local churches.
Then... decision time. One of the great benefits of free flight benefits! If the kids (and us) are tired out, we can start heading back to the US by going back to Rome, perhaps via Siena. But if we have two days left in us and our legs will hold out, I'm planning Venice for two nights and one full day. This would be entirely a last minute decision so it will also depend on reasonable lodging as well. Venice would simply be the major sights and a vaporetto ride or two before heading to the airport on the 19th to go home.
I've done plenty of research into restaurants kids would enjoy, and, most notably, we're not planning more than one or two real sit down meals as I don't think the kids would sit through those more than that. (They don't like the sit down meals on cruises, so I don't think they'll sit too long at dinner.) But I'll take any family and kid-friendly advice on restaurants or other sights that I have not mentioned.
I know it's a very rough itinerary. We've always traveled that way with great success. No solid plans for the most part, other than hotels and the Vatican. We'll see how well we adjust to the jetlag and go from there. And if we miss something, it will always be there when we return!
Thanks for any input!
Scott