Feedback on itinerary for family of 5

Have you been to Europe before? The heat at this time of year will be exhausting, along with the crowds. You will need afternoon breaks from the heat.
I think you have too many destinations. There's no time to slow down, relax, do laundry, nurse the inevitable cold.
I'd eliminate the day trip to CT, it just sounds exhausting in the heat.
Start in Venice, it's easier to fly into, and work out the jet lag. Rome is too chaotic and hectic for the beginning, IMHO.
What if your incoming flight is delayed or canceled? You need to build in an extra day in the front. Flight cancelations , delays , and schedule changes are increasing, post Covid.
Keep both Lake Como and Venice, where there's peaceful, beautiful scenery. We stay in the Cannaregio area of Venice, on the back canals, where there are no crowds.
Have you researched lodging? You really are a bit behind for summer reservations, so that may influence your itinerary, especially for five beds.
Have a great family trip!

Goodness you are seeing a lot on this trip! Especially when you factor in summer crowds, heat (last July was horrible in Rome) and grumpy teens. I have teens who are well seasoned travelers but yes they can be grumpy!
I think you can still see a lot in your time though. What if you skipped the CT/Pisa and added those two nights to Venice? Two nights in Venice is not enough. Also halfway through your kids may need an afternoon "break" from their vacay. I wouldn't add more time to Milan bc there's less to see. (don't forget the Duomo) Or you could add 1 night to Rome and 1 night to Venice.
Def go in Rome and out Milan as it will be hotter and busier further south the further summer gets on. Try to go as early in June as you can!

My husband, 15 year old and I will be Italy late June/early July as well. We have been to Europe many times as a family, and in my opinion, your proposed itinerary is much too rushed. If it were me, I’d split my time between Rome, Florence and Venice, and maybe consider adding Lake Como OR Milan OR CT but not all three. You may even want to consider splitting your time between 2 locations and taking day trips. It sounds like this will be the last big trip for your family before kids head to college, so reduce the stress as much as possible! I do agree with starting in Rome and traveling north to avoid the heat if possible.

I posted our itinerary a few weeks if you are curious. https://community.ricksteves.com/travel-forum/italy/pick-up-the-pace-italy-itinerary-advice-for-the-slow-traveler

Beyond a certain point, you do not see more by adding destinations; you see less because you're spending excessive time sitting on trains and buses, checking in and out of hotels, and traveling between hotels and train/bus stations. When you have six destinations crammed into a trip that's only 11 full days long, you are not seeing more.

You will almost certainly not be able to book an afternoon flight out of Milan that's late enough to allow you much morning sightseeing time in the city. Your airline will tell you to be at the airport 3 hours before departure time (if not earlier). Almost all transatlantic flights and feeders depart from Malpensa Airport, which is a long way (30 miles) from the city. To allow for transportation hiccups, you'll need to add extra time for the trip out to the airport, and the scheduled travel time for the trains between Milano Centrale and Malpensa is already 52 minutes. Then you need to add time to check out of the hotel and get to the train station and extra time to get from the Malpensa train station to your airline's check-in counter. I'm conservative when I'm facing the prospect of missing an expensive transatlantic flight, so I'd be leaving my hotel 5 hours before schedule departure time. And before that was breakfast. It's a rare American indeed who manages to accomplish any sightseeing on the morning he or she flies back home from Europe.

Depending on where you're staying in Milan, getting a train from Milan Cadorna Station to Malpensa might be faster. Do check on that.

I agree with everyone that you have too many destinations. Each time you pack up and train somewhere you are losing a fair amount of time. Assume you will be back! I would either drop Venice or Milan. Or ( gasp) Rome. Agree with you that Rome is nicest for the end of the trip, and it will probably be hot whenever you go. You are trying to fit in all the big sites and with your current itinerary I think by the end of Florence will be quite exhausted. By my count you have 12 nights?
I'd do one of the following :
Venice 3 nights- Cinque Terre 3 nights- Florence 2 nights- Rome 4 nights
You could replace Venice with Milan and have 2 nights in Lake Como 1 in Milan.
Or you could do Venice- Florence- Cinque Terre- Milan and Lake Como and leave Rome for another trip.

Thank you so much for your feedback, everyone!! I obviously need to give this some more thought and probably drop at least one destination. I may write again if more questions come up - but thank you so much for taking your time to share what you think - it means a lot and has been very helpful.

The golf cart tour in Rome is very fun, but I'm not sure about doing it on your arrival day. But it could work, if you're not too tired.

Not sure if it would be wise to do the Vatican and the Borghese Gallery on the same day. That is a lot of museuming for one day! And your feet might really hurt enough just after the Vatican Museum and the Basilica.

Can't comment on the other cities, as I haven't visited them yet, although I do agree with the others who say you have too many destinations. Too much time on trains and too many cities in too short a time can make your trip a blur that you will barely remember. Cramming too much into your days can also have this effect. You want to be able to have time for what you have done and seen to sink in. You want to be able to appreciate and think about what you've seen before you are off to your next thing.

and just seeing your planned days......I like "culture" and I will definitely be on multiple guided tours through museums and historical sites over a long trip, BUT I won't schedule more than one major "thinking activity" (learning, history, art, listening, etc) per day, unless I REALLY need to.

I think last time I was in Rome I had only one day where I did a 10-12 tour and a 2-4 tour and I knew it would be a long and tiring day, having much of the next day to recover. I would definitely agree to put the "walk by and appreciate" sites on your itineraries, but I would use them as part of my "decompressing" after an in depth tour. Like a morning tour of the Coliseum, and then a wander through the centro storico to browse and see the Spanish Steps and the Trevi Fountain. Nothing you have to book tickets for, but its neat to "do" where you can fit them in. Your Florence day where you put the Uffizi, Duomo, and Palazzo Vecchio has at LEAST one too many big sites, possibly two too many depending on your family's capacity for taking in information. I wouldn't put the Borghese gallery after a LONG morning at the Vatican, I would want to faint right there in the park in front of the gallery from brain fatigue.

I want to punch someone on my arrival day by about 6pm, and having to wait until 8 (in the south) to eat dinner is ROUGH. I wouldn't shy away from doing SOMETHING that day, but not much that involves thinking. Possibly a good time to do a Rick Steves' walk around from the guidebook? That is me, you might be better at travel to Europe than me (I am VERY worried about my next 5 hour layover during that awful time waiting for my next flight through Heathrow in July haha I will arrive at my destination and want to collapse).

There are a lot of "maybes" in your schedule, I hope that means you will decide way ahead of time to purchase tickets in advance or not, because arriving into town and wanting to do those things won't be easy. Good thing you will buy your train tickets WAY in advance and will be able to make those plans!