Welcome, this is a big question. Generally europe goes on hoiday at the end of July with August crowds. Weather varies but southern Europe can get to 25-30C while northern 20-25C.

One thing you could do it to book an appartment or gite so that you can eat in or eat out. With a pool it means that the kids are safe and happy. Interesting places everywhere but if you want the cool then look at Northern France, Holland, Germany close to the Mosel/Rhine.

Generally English is spoken well in Holland and in tourist areas in Germany and to a lesser extent France.

Public transport is clean and easy to use in the area. So have a look at a good book say Rough Guide Europe and work out which bits look interesting and come back

Are you inclined towards any particular country/countries, as it is rather a broad question, and would you like to visit places that would include a funpark, waterpark, aguarium, boatrides, beaches, cable car rides, museums that might interest them, like science and war musiums, palaces, historical centres, gran prix races and football matches for older ones, etc that might appeal to everyone including kids? Would the other four be grown-ups, or maybe teenage kids?

Do you prefer resort hotels, maybe just outside cities and towns, countryside accomodation, accomodation in cities, on mountains resorts, etc etc.

I have always travelled with my family on holidays since they were little, and I do know that one thing they really used to hate was hours and hours of travelling, the younger they are, the harder it was to make them sit still, so wherever you go, take things that would keep them occupied.

One last question, how long is your holiday, and do you prefer to stay in multiple places?

I would love to suggest Pari. Paris is a perfect destination for family although it would be expensive family vacation especially in July.