Savvy Trades and Investments

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Definitely, Rome! It is absolutely unique. There is no other city in the world with so much history. They don't call it the "eternal city" for nothing. 5 days in Rome is sufficient, IMO. 
I would recommend going from Paris to Rome through the most fancy regions of Europe - (1) Provence/Cote d'Azzure in France (wine region and top seaside region in France) and (2) Tuscany (also a wine, hilly region) with the city of Florence. 
Alternatively, you may consider Barcelona in Spain, Lisboa/Porto in Portugal, Prague in Czech Republic, Krakow (and Ausschwitz concentration camp) in Poland or visiting Switzerland (the Alps mountains and Swiss cities like Bern or Lausanne). Many alternatives, depends on what you prefer for your family.