Do I have to reserve 2 rooms if we travel: 2 adults+ 2 children?

The lesson here is to avoid those big-name hotels. It is absolutely possible that they only have rooms with double beds and nothing larger. I did a quick search on a couple of hotel-reservation websites and found numerous hotels in Rome, for example, that would accommodate four people. Some of them advertised them as "Family rooms", but absolutely they are available. I guess you might want to use something like Trip Advisor to check out non-big-name hotels that can accommodate your family.

Yes, unfortunately the Western chain hotels have very strict limitations. Almost all of this is due to the fire codes in these cities/towns.

Further, it seems that Italy is very strict and very expensive. A roll-away in a lot of the SPG (Westin, Sheratons) hotels will easily set you back 70+ euros a night.

Here are a couple of suggestions:
for Hilton, email the hotel directly and ask if they have family rooms. Some Marriotts allow 4 in a room (Vienna, London) though not the ones in Italy.

For more details on these hotels, go to Flyertalk.com and check out the sections under hotels. Unfortunately, this is a limitation of the Western chains especially if trying to use points. Your options are paying for 2 rooms or going with a smaller budget hotel.

Fire Codes are 4 in a room.
Can you fit one of the kids in your bags? ;)
We did 5 in a room in Germany, Paris, London,Italy.
We did rent some as Family Rooms.

We have traveled to Italy many times with our kids. We ALWAYS get a quad room. I also would never go to a western style chain. if you are interested in a nice reasonable, vy clean, great location, with great breakfast in Florence, try Hotel Casci.
ps. my husb is from Tonawanda. we are in Buff a lot.

There are hotels with quad rooms, you just have to look for them. Though it's true, they aren't as common as in Northamerica.

However, our solution was to rent vacation appartments. That gave us more room and can be quite a bit cheaper than a hotel, especially in Rome.

We are a family of four traveling to Rome, Venice and Florence as well and had no trouble finding quad rooms for families (after some research that is) I used this helpline, Trip advisor and a book called "500 places to take your kids before they grow up". It is by Frommer’s. I really like this book for several reasons; it also gives you names of hotels that are family friendly. I didn't use it for Paris since I have been there before, dream of living there (someday) and wanted that "I live here, I am a local" feel to the trip, if only for a few days. lol :) I also rented an apartment in Rome (thanks to advice from a fellow traveler on this helpline) but that was for different reasons, not for the lack of options.
Good luck
Ps/ Someone suggested Hotel Casci it is in the book I mentioned. We booked there, and they are wonderful to deal with.

I concur with Beatrix. We are leaving for Italy in 2 weeks (yay!) and are a family of four with 2 adult sons. In each case we opted for an apartment because the quad rooms were usually a double bed and a pull-out couch. Since both of my sons are over 6' and are not the least interested in sharing a bed (imagine that), we had to find places with a total of 3 beds. The most economical way for us to do that was to find 2BR apartments. Feel free to PM me if you'd like the names of the places we have rented in Venice, Florence, and Rome.

Like Melissa said be sure when you talk to different hotels that there are beds not a pull out. Our boys are younger (not 6ft yet) and don't mind sharing. However, I didn't want them on a pull out. The places we found all have beds.. some a queen and two twins, some two doubles... etc...

I just booked a room for our family of 5 at the Hotel Adler recommended by RS in Rome www.hoteladler-roma.com and we will be staying in their "family room". Good location and much less expensive than 2 rooms. Stay in family run hotels if you can vs. big chains!

Thanks to all of you that replied.What great answers! Any good QUAD rooms in Venice and Florence?
Virginia

We had a very nice quad room in La Scaletta in Florence (summer 2007). They must have at least two, because my brother's family also had a quad (at the same time). The hotel was very accommodating in handling our big family group.

We are a family of four traveling to Italy and France in May. I have booked quad rooms in bed and breakfast facilities in Florence, Rome and Venice. Great prices. As someone suggested, you can get excellent unbiased information on Trip Advisor. There is a tab at the top of the page to search either hotels or bed & breakfasts. Have fun!

We were 5, and had a great holtel in Venice.
I will look up the name when I get home.
Rome we did an Apt. and we also did a farm in Parma.

Make sure that when you approach a hotel, especially smaller family run places, explain your need, that you are a family and the ages of the children; rather than just asking for a Quad. That will allow more flexibility, since a quad needs to fit four adults, and you could do with a triple and a cot, or they may have a larger double that they could bring something in for the kids. I have even had places like this tell me that they can't help, but recommend another place close by that can.

Virginia
Rome is tough but we have stayed with 4 in Venice at the Hotel Flora which is a clean well reviewed 3 star near San Marco. In Florence, we had a suite at the Antica Torre di Tornabuoni, but there are several that can accomodate 4 including the Hermitage, the Michelangiolo among others. They are also very affordable now. Good Luck