Hi, Peter. I’ve travelled to those countries extensively, so this is something that I know a bit about.
The first observation I’ll make is that this is quite a long trip! That’s good. However, you’re also visiting an awful lot (comparatively speaking) of places. Without getting all “You should replan your entire vacation!” on you, I think you should make sure to account for the amount of stress having that many destinations and that much inter-location travel is going to add to your trip, especially with three kids and 2 language changes in the middle of them. At each change, you’re going to have to deal with finding your way around a new city, finding your hotel, checking in to your hotel, finding that the hotel lost your reservation 20% of the time, etc. You also don’t say whether you speak Spanish, French, or Italian, and that may make a difference in your planning.
My advice would be this:
(1) Cut the trip number of stops down and think in terms of longer stretches in fewer bases. If you have a destination you really want to see, make it a day trip from your base. Bologna, for example, is maybe 90 minutes from Firenze by either train or car (probably less, but i’m allowing for friction). Why add a complete stop when you could stay in one and day-trip to the other?
(2) All of your destinations are urban. That’s cool. But, if it’s the sort of thing you like, you might consider planning one more pastoral base to explicitly allow for some down time. Particularly in northern Italy, Florence is very touristy, and there are lots of interesting options that have that Tuscan feel while being a lot less frenetic. I mean, I love Florence, you should go, but it’s the quintessential example of a good place to go into and then leave rather than a place you should sleep. Whereas when you’ve rented a tuscan villa for the week, you can still go there, or go to Siena, Montepulciano, or Lucca (which is lovely, by the way) or you could just say “You know what? Screw it”, and sit there with a glass of wine and do nothing. I suspect that particularly after a week with 3 kids in Paris, you might want some downtime.
(3) Venice is a sewer. Skip it. IMO.
(4) April in Rome will be wet and a little cold, but it’s the perfect time to go. Oranges will already be ripe. There’s more history in Rome than anywhere else in your trip, so my overall Italy advice is to favor Rome over the north.
(5) I’m not gonna try to talk you out of Paris, but ok yes I am. Go from Spain to Italy by making a broad sweep across the south of France. Visit the Dordogne, Provence, ride huge white horses through the wildlife preserves in the Camargue. Visit Avignon. Spend a day or 2 in Paris if you need to check the box off your list. But you don’t need Paris, because you’re going to Rome, and the coffee will be better in Rome.
(6) if you’re driving/renting a car, for the love of god pay extra for the comprehensive mega plus super bonus collision insurance. This is probably the best reason to take trains everywhere, which may conflict with my #2 above. But that’s the tradeoff.
I can give you specific restaurant recommendations for Firenze and Rome later in the thread once i find my notes.
You will have uncomfortable encounters with Roma vagabonds, but I don’t think it’s anything to panic about. It’s not worse than the typical encounter with homeless people in NYC or SF, as long as your kids know not to, y’know, wander off with them.