how much money would a family of 4 need

Your information is so limited that at best it is a shaky guess. I would plan at least 200 to 300E/day excluding transportation costs between cities.

Can you give us a bit more information about what you intend to do, activities, whether you plan to eat in restaurants three times a day, or picnic in your hotel room, take trains, or cheap flights, etc.? There is a big difference in the budget if you book trains or flights well ahead, or if you only plan one restaurant meal a day, etc. The more information you can provide, the better answers you will get.

... and the ages of the teens. Big difference in eating capacity of a 13 year old and an 18 year old... Are you picknicking or gastronomes?

London is very expensive. Wagamama is your friend. This is a small chain of Asian-fusion restaurants with several locations in London. Our girls loved this place at age 12 and 16, and still loved it at 18 and 22. Assuming you are staying in hotels, take advantage od the full English breakfast and you can make do with picnic sandwiches for lunch. I cannot speak to Paris as we had an apartment there and did not dine out. Last summer in Italy our food expenses averaged 120 euros for a nice dinner for the 4 of us, including wine. Breakfast was at the hotel and lunch was 40 or 50 euros. Add another 10 or 15 euros for daily gelato.

Hard to answer. First question by transportation do you mean just the subway/bus in the 3 cities or do you also mean the cost of transporting between the cities. Obviously the latter cost more. But I am guessing based on what you have said that you might be on a tour. Some budget tours use hotels well outside the city. If that applies to you than the cost of a taxi the city is going to cost more than the cost of simply a bus pass. Assuming you only need local you can find info on local transportation at http://www.tfl.gov.uk/modalpages/2625.aspx http://www.parismetro.com/ http://www.romebuddy.com/givesadvice/metropasses.html And figure out the transportation costs for your family based on what you want to do. Of course forging public transport and using taxis will cost more. As for food....how much does it cost to feed your family in Irving TX? Figure it will cost 25-60% more. Bearing in mind how do you plan to eat....buy cold cuts and bread at the store and make picnic? eat at McDs? Go to the nicest restaurant in town? Either way it is going to cost more in Europe than in Irving to use the same method. But the largest factor will be how and where you eat so nobody can tell you how much to budget without knowing your dining habits.

So far on our Italy/France/Belgium/England trip, we have had breakfast at all of our B&B's and hotels. But we have eaten 1-2 meals the rest of the day at a cost of 10-11 euros per day for 2 adults and 2 children (ages 20 and 25). The food seems reasonable but the drinks will kill ya! There are NO refills either! We all carry water and haven't noticed anyone looking at us funny using it where we eat (after we have purchased our meal). I noticed grocery store/markets, but they are tucked away along with everything else in town where we picked up snacks/drinks. We had a eurail pass and it was very easy to use and people were very helpful. Get your next leg booked a day or two in advance! We will use our Oyster card in London, didn't stay in Paris, but walked 6-10 miles in Rome everyday and didn't take any transportation.

The pharmacies are very helpful. I developed a rash on the first day and got what I needed. They had moleskin for the 25 year old that developed blisters early. It was hot (90+) & muggy in Rome, and I think that contributed to that.