Have done this a few times. Where are you going in Italy?
At Easter we drove from Yorkshire to Liguria. We prefer to just get on with it and get there as quickly as possible, so we did it in two days each way (with a stop in France).
On the way down (if you remember, weather was terrible at Easter!) we had a terrible journey. Snow in Mont Blanc tunnel caused 4-hour queues on the French side. Luckily we heard this on the French radio in a service station and diverted south all the way down to the Riviera and along the coast into Italy. That was is very very long, but was better than sitting in a 4-hour queue (and the weather was better than it would have been in the mountains too). On the way back, we did come via the Mont Blanc tunnel and it was a really good journey. Day 1, left about 7.30 a.m., got to the tunnel for about 11.00, stayed overnight in France (near Laon). Left next day at about 9.00 a.m., got train back to the UK and were at home in Yorkshire by about 5.00 p.m.
Have also driven to Friuli and to the Alto Adige/Sud Tirol, both via Germany and Belgium (getting the ferry Hull to Zeebrugge, which is an overnight trip so you arrive in Belgium at about 7.00 a.m. and can just get on the road. (Only convenient if you're in the north of the UK, though.)
I have two dds who are 6 and 8 now, but have done these trips since they were 2 and 4. We now have an in-car DVD which we put on when we are doing these long journeys, but we didn't have it the first time we drove to Italy (admittedly only just Italy - Alto Adige) and it was OK, though the 2-y-o found it a bit trying at times.
Quint... pre-kids we did it by motorbike too. Did a huge circular trip... France, Germany, Austria, Italy, back through France. The best bit was when we nearly ran out of petrol on the Italy-France border halfway up a mountain (it was the time when the Mont Blanc tunnel was closed) and had to freewheel down to the nearest town to fill up!