best way to travel between cities with children?

Trains are very reliable, except when there is a strike. But these can happen in any European country. So keep you eyes and ears open.
Trenitalia does have discounts for children of various ages.
Also look at Italotreno which runs high speed trains on the same tracks.
Make sure you can get reservations to see the "Last Supper". It would be a shame to make a big detour and not be able to get in.

Read this from Italotreno, looks like kids under 5 travel free and there is a family fare for kids under 15.
http://www.italotreno.it/en/train-offers/Italo-Famiglia

It should be pretty inexpensive to travel by train with point to point tickets. Kids under the age of 4 travel for free. Kids ages 4-14 travel for 1/2 price. The issue of booking tickets ahead of time from the Trenitalia site is that you can only book 5 tickets at a time so you'd need to do it as 2 transactions using 1 adult each time. You might also look at the captaintrain.com site for booking tickets that several people on this forum recommend. Maybe they would let you book more tickets as one transaction.

On trenitalia.com I used a random date in March and chose 1 adult and four children (ages 4-14) and I got a total price of 38€ for Venice to Milan for example.

Thanks so much - I will check those out now! We got the tickets for the last supper a few days ago :).

For activities in Venice, you might want to look into rowvenice.org for the older kids - learning how to row standing, as the gondoliers do. There are also opportunities to learn how to make Venetian-style masks - one website I ran across is camacana.com.

When traveling by train, plan carefully, ahead of time, how you will move your luggage and your kids. Often (not always) the trains are only in the station for a few minutes, both entering and leaving. So you should be ready, bags in hand, and kids in hand to the extent possible. I assume you'll have child carriers of some sort for the youngest two. How many pieces of luggage will you have, and do you have enough kids to pull the bags that you won't have the hands for?

I assume that you've already confirmed that there's a left-luggage office in Milan for you to leave your bags while viewing the Last Supper.

Not intending to alarm you, but pickpockets do make a living in big cities in Europe. They watch for people who aren't keeping eyes and hands on their bags. Since I hope your eyes and hands will also be on your kids, make sure your money and travel docs and things like phones are tucked securely away. One advantage you'll have, I think, is that pickpockets may assume you're a European family traveling, and more "local." We felt that way when traveling with our kids (though only 2 of them).

When we took our kids to Europe (they are now 17 and 20yo), we figured they could make pizza or gelato or frescos at home (you could do it together in preparation for your trip). Consider activities that can only be done there, even if it's just buying a cheap soccer ball and letting them play with other kids in a square in Venice, for example. We went to the mercato in Florence and bought one type of cheese (fresh pecorino, I think it was) from several different vendors, then did our own taste test. My daughter and I would share a three-scoop of gelato; I would pick the flavors, and she would try to guess which they were. You could have them race around the Circus Maximus in Rome. In Rome, visit San Clemente - one church built on top of an older church, which is built on top of a Mithraic temple, which is on top of an ancient Rome home. And the cat sanctuary at Torre Argentina, which also happens to be the spot where Julius Caesar was assassinated. In Florence, go to Piazza della Republicca in the evening and watch the (mostly American) buskers sing American songs. Venice itself is so different and so magical, that your kids may feel that just walking through the narrow streets and along the canals. Speaking of canals, come up with a way to keep eyes and hands on your youngest children while along the canals - there aren't always walls between the streets and the water.

Enjoy!

On Trenitalia, you want the Bimbi Gratis fare,k where kids under 15 travel for free with accompanying adult. The website CaptrainTrain.com is easier to use than TI, but I have no idea if they offer this fare, so double-check.

The trains are VERY reliable. If there is to be a strike, it is known in advance, but the high-speed freccia trains are not affected. They continue to run -- at least they have continued to run through the strikes I have observed.

We had good luck with all of trains in Italy in summer 2014 (rome to lucca to pisa to venice).

Yes, the point about the trains entering and leaving quickly is a good one. It can be kind of hectic in those moments.

In Florence, we saw gypsies scamming people to "help" with their luggage. One woman tried to grab my kids luggage (although he was handling it quite well), but a firm NO and she moved on.

I only mention it there because our friend who is from Italy warned us about Florence in particular, and when we were on the train, the conductor made a big point of warning us. It wasn't a big deal, but I was glad I had a heads up and was ready.

Not sure what you are planning to take for luggage, but I would make it as small as possible (NOT bigger than carry on) and be sure everyone can manage their own stuff (obviously except little ones, but get their stuff inside someone else's).... we have seen many people on trains seriously struggling with oversize luggage (including the ones who got gypsie scammed), both getting on and off, and trying to find somewhere to put it. I can't imagine dealing with that plus many kids, some babies. Just pack light, do laundry. You really need less than you may think. Trust me, if you have larger than carry on luggage your train experience is going to suck.

If you are going for spring break, get your train tickets ASAP, prices go up. I can;t remember when they open but its 60 or 90 days, so they are probably ready.....

And I second rowvenice.org. Super fun. We did the gladiator training and it was "meh". The little artifacts they have were interesting, but the class was not so good.... I will however add that I think there was a bigger place we were supposed to do it, but they were filming in there or something, so we ended up out in the courtyard, and it is was kind of raining.... so that probably skewed the experience. The guy that ran it though was really nice and interesting.

Have a good trip!
Kim

I second the suggestion of giving the kids a cheap soccer ball for playing in the Venetian squares with the local kids. It's really wonderful how kids can get out and play there with no worries about cars. Also wanted to suggest that they'd most likely love taking the vaparetto to visit some of the islands of the lagoon: Burano, Torcello, Murano.

The Italy rail pass also gives free kid benefits, but probably won't come out any cheaper nor more convenient than the point-to-point kid deals already mentioned. The second class pass for three travel days (you're only using two) costs $155 per adult, $149 per youth, and up to 2 kids (ages 4-11) free with each adult. All your trains will be fast trains, so seat reservations with a pass would be €10 (or $12) extra per leg and per person age 4+.

Again, under 4 always free on any train but they won't have an assigned seat and will sit on your lap (or maybe run in the aisles) if there are no open seats nearby.

I'm going to skirt all the warning stuff about pickpockets and whatnot. If you do some reading, you'll know how to avoid those pitfalls. Italy is NOT a den of thieves, and Italians love children.

You've also gotten the info you need about the trains.

As far as activities for young people, I wouldn't spend too much time on that. There are no "must do's" other than just being there for them. Given space to be children, they should be able to create their own fun. I think your bigger challenge will be finding middle ground between your teenager and your pre-school youngsters? You might want to consider the occasional divide-and-conquer approach where one of you takes the older of the kids off for some history and culture, and the younger kids go blow off energy at the park and have a nap?

We found the trains very reliable when travelling with our kids - mind you it was two kids, so pretty easy. The only two issues I can think of is watching your bags with pick pockets (having said that we only saw that in Florence - saw far more thefts in France than Italy) and getting up the 2 steps into the train with luggage and children. My kids were very independent 10 and 13 years olds when we went so we didn't need to do too much to entertain them. They wanted to see the same things as as - except they did all the ordering etc in restaurants and shops to force them to learn Italian (Yep they were far better than us at the end of the trip). Have a great time.

Hmmmm, how to travel in Europe with 7 young children? Well, in The Sound of Music they just walked over the mountains to freedom, and then settled in Vermont. Can you guys sing?

You have all given such INCREDIBLE advice and direction. Thank you so much for all of your thoughts and ideas (small luggage, get train tickets soon, rowing in venice, soccer ball in Rome, etc.) This is getting me more and more excited! THANK YOU!!

... and I laughed out loud at the climbing the mountains. Not much of a singing family... but we can play stringed instruments like nobody's business... I wonder how 2 cellos would fair on the trains... ;).

Thank you so much once again!!