Rome v Florence 7 days

My personal opinion is that I would just base out of Rome and do a couple of day trips. You lose time traveling from location to location, especially when that many people are involved that you have to wrangle (lol).

Given the composition of the group and your 'impedimenta', if you do choose to spend time in both Rome and Florence, I would do all the Florence days at the front end and your Rome days at the end. That makes for just one move vs. two if you were to split it the way you mention.

It’s easy to fill 7 days in Rome and barely scratch the surface
I’d stay all 7 days there
Those that want to can day trip to Orvieto, Ostia Antica, Tivoli etc just some ideas

Florence as a day trip is just not appealing to me
Deserves a minimum of 3 days.

Moving is a pain but if you must split stay then head to Florence first put all Rome nights at end

I would vote for 7 full days in Rome. In someways, Florence is very similar to Rome. For a break I would do a couple of day trips out of Rome. Second, will you be in Rome over a weekend? The toddlers will slow you down especially if there are naps involved.

Another option would be to find a really good agriturisimo north of Rome and rent a car (or two) to do day trips out of. Your travel party is just a little too large to haul around from place to place, and the kids throw another dimension into the trip. So many farms in the region have apartments and rooms for rent as a source of additional income.

Someone mentioned Orvieto as a good day trip. That would be a great place to stay outside of since a train gets you into Rome in 70 minutes. There are many other hilltowns in the area that are very interesting. Sometimes you just have to hit the highlights.

As far as luggage goes, limit all travelers to one rolling bag. You don't have to take the kitchen sink with you.

The good news is that before you know it, those toddlers will be old enough to have their own rolling luggage. Florence is my second favorite place of anywhere I've been, so I'm in favor of splitting the time and actually spending more time in Florence because it's more compact and easily walkable than Rome. I can share my own experience taking an 18 mo old on this trip with my 70 yr old inlaws. We stayed at Hotel Museum, right down the steps from the Vatican Museums so we could take turns staying with her in the hotel while others went to the Vatican Museums. Each of my inlaws had one large rolling bag and one personal item and were actually able to help with our baby's stuff.

Thank you
I thought about going straight to Florence but after the flight I don’t think I’ll be able to get everyone on the train right away, already got our tickets into Rome.
We will be there for a weekend but the toddlers don’t take naps anymore, I like them more than they do. Lol. My wife and I were in Rome for three days on our honeymoon and missed it the moment the train left the station to go north. I’m leaning towards Staying based in Rome now. Just soak up as much of one city as possible and not feel rushed. It might just eat at me that I haven’t been to Florence yet.
I think the kids won’t care. My teenage daughter is going to love Rome.

There’s a direct train from Rome’s Fiumicino Airport to Florence (2h 30m) departing at 1:53p.

Based on your group size and composition, I (somewhat reluctantly, because Florence is my favorite city in the entire world) would recommend you spend all your time at a base in Rome. There just isn't enough time to justify wrangling a large party to a new location when there's so much to see and do in Rome.

Every kiddo is different, but mine (he just turned 5) takes at least a few nights to settle into a new sleeping environment, and we find we do better when we home base. It's just a more comfortable environment for him, plus there's less stress/pressure on me to make sure we don't leave a beloved toy or stuffed animal behind when we change hotels. I'd also strongly strongly strongly recommend that you condense your luggage as much as possible.

Speaking from experience (we've taken our kid on 3 trips to Europe so far, including Italy when he was 2.5), you will want free hands more than you will want whatever is in that suitcase. If you need larger items like a pack-and-play, crib, or car seat try to rent it upon arrival. Buy a few new toys, toiletries, diapers (if you need them) snacks, etc. once you land in Rome and get settled. Rent an apartment with a washer or do laundry in the sink. We've done all our trips to Europe, for 3+ weeks each, with my son and I sharing a carry-on size suitcase. Pack just the necessities, and realize you can buy absolutely anything you need if something unexpected comes up.

Most importantly, have a great trip!