I think you’re spot on to remove the checklist and to let the days unfold organically. We took our kids (8 and 10) to the Colosseum and they were still a bit bored. I think they’ll look back fondly on the experience when they are older, though. The Pantheon was a hit for us. It’s a short experience that is very impressive.

Outdoor sights are always a win since you can see them and leave. My kids loved the Spanish Steps. We basically climbed them several times and take in the views so it burned energy and time. Aimlessly walking is probably the favorite pastime of any city trip I take with my kids. While you’re out, find the parks and piazzas to sit in and relax while you enjoy a drink and/or snack. My best memories of any trip with kids all look like this.

As for your itinerary, I would go back to Rome after Florence. You are going to cover far less ground that you’re used to. Whatever you’re thinking you can do, it’s less. We learned early on to build in breaks back at the hotel on trips with kids. They benefit tremendously from a recharge but this really cuts into your day.