Car Rental from Italy To Southern France in July

A few years ago, we went by train from Milan to Nice, and it wasn’t a fast train. It took all day. If you did make it to Nice by train, and wanted a rental car at that point, at least you’d just be renting in France, and not paying for picking up in Italy and dropping off in France. How about breaking your train journey into two separate days? Or flying from Milan to Marseille, and picking up a car there?

We’re visiting Southern France in July, and staying in Airbnb apartments - affordable, with kitchen and laundry available.

Look at car rentals at Moncton, just over the border. The train from Milano Centrale to Menton takes 4.5 hours, with a single change at Ventigmilia.

....Car rentals from Italy to France are outrageous....... That is because of the drop fee. Most rentals between countries are outrageous because the vehicle has to be returned to the original country. I have no experience with it but it has been recommended here that you drop a car in a border town, take a taxi across the border and rent on the other side. Sounds like a lot of work. Personally I would rather have a long train ride than a long car ride. On a train you move around, have rest rooms, snack bars, etc.,,

As Americans we just automatically assume that cars are the best way to get around. Europeans will tell you that trains are the best way to get around, because they have systems that actually work.

Or nowadays sometimes it makes sense to take a flight like Ryanair although it's not completely pleasant.

I am hoping they have looked into the car seat requirements for 3 children that age, and figured out how to install all 3 car seats in the rental car.

Travelers are heavily charged for picking a car up in one country and returning it to a different country. This is not a new rule. It is not just Italy to France rather the fact that they are two different countries.
I would try to rebook your flight to France not Italy.
We have used this strategy: Pick up car and drop off in same country. Or Taxi across border, pick up a car in the next country. Repeat as needed. Car rentals with pick up in one country and return in another country are high for a good reason. We were quoted a 1000€ fee to do that ( Portugal to Spain) so we paid a taxi 150€ to take us across the border to pick up a car in Spain.
The reason for high price is due to the fact that the agency where you pick up the car would have to send someone to pick up the car in the other country and bring it back to its original country. It isn’t just car rentals from Italy to France but for any places in different countries for pick up and drop off. This is nothing new.
You can avoid this by flying into France or doing the drop off one country/ cross border/ pick up in new country strategy which we have done many times.
With the ages of your children the easiest would be to fly into France, and either Marseille or Nice airports would work well. Rent the car there.
Or fly from Milan to Nice and rent a car there. Small, easy airport.
Accommodations in Provence tend to be on the high side. Perhaps other posters know of a less expensive property. Google “less expensive hotels in Provence” as a start. An Air Bnb would be more affordable and comfortable for a family of five.
For car rentals we always book through AutoEurope. Good luck with what you are planning!

juliabagg,
Although it may be difficult to find a place at this point in time, you could try checking gites-de-france for rental of a house or apartment to stay in whatever town you settle on in Provence. They operate a bit like AirBandB, but have been around longer, are very reliable and have a variety of places to stay, from rooms at a real B and B to large houses. Southern France covers a large area...the Riviera (Nice) and the Luberon, Drome, Provence Bouche de Rhone. When deciding where to narrow down our trips, I usually get an old-fashionbed paper map, spread it out, and see where things are in relation to one another. It gives me a better idea of distances between places so I can eliminate outliers, get a better idea of time to drive between places, and what I can reasonably find time to visit. (e.g. Pont de Gard is close to Nimes, but not too far from other charming towns as well.) What you finally decide may help you determine the mode of transport from Milan. Suki has made some very good points about this, as have the other posters.
And Lola brought up a point which I, and maybe those of us who are past the small child ages, forget...car seats! Rules are very strict in France about secure seating for the little ones. And in Italy as well, I would guess. Something to consider, especially because larger cars like minivans are difficult to drive in many smaller villages. Parking is problematic also. (I speak from experience. In 20012 we had an American sized minivan because we had a relative who was elderly and mobility impaired. It was no fun for my poor husband!)
I hope you are able to get your plans settled and that you have a wonderful trip! Bonne chance!

Suki is right: it is rarely affordable to rent a car in one country and drop in another. When faced with that situation, I usually take a train across the border and rent from there. In this case, train to Nice, and rent from there.

And Lola brought up a point which I, and maybe those of us who are past the small child ages, forget...car seats!

I mentioned this in the other thread about Bavaria. Must have the correct mountings for the seats.

You might PM the poster of the recent report of Nice and around Provence. The three kids are a bit older than yours but they might have some insight about car and car seats.