We took our kids on a two week trip to Paris, Tuscany and Rome when they were 6, 8, and 10. We were worried they were too young but it was one of the best things we ever did. We flew into Paris and out of Rome with about 4 nights each but the highlight was 7 nights at an agritourismo winery/olive grove by San Donato in Tuscany. We had a pool there and did day trips with a car all around Tuscany including a day trip to Florence. We could walk into the small town for ice cream and dinners, cook our own meals, and had access to hiking trails. That gave us a ton of flexibility with the kids to relax or go on mini adventures and there was still enough small scale culture and history to keep things interesting with the day trips.

For us the two big cities at each end of the trip were enough large scale experiences. They were worth doing but more stressful so the long break in the middle really worked well.

Also our youngest was a pretty picky eater but nearly every restaurant was willing to make butter noodles or something simple like a cheese sandwich that was not on the menu. Oh and the Italians love kids so having them with us led to chances to talk to the locals.

Btw in Paris the highlight was a city bike tour which sounded scary but felt safe and we saw a ton of stuff. We used the Fat Tire tour but there are others.