In my opinion, the best Italian locale for kids is Rome, followed closely by Venice.  A visit to these two cities can be followed by some R&R in either the Amalfi Coast or Tuscany.  Puglia or the Dolomites are more off-the-beaten track, but equally great options after Venice & Rome.

There are many touring and activity options for children and teens in Italy.  In addition to organizing family-friendly guides for the major sites, I can set up cooking classes, scavenger hunts, Vespa tours and more.  Kids don't realize they are learning!  My kids took a gladiator training class one morning, which made the Colosseum come alive when we toured it that afternoon.  They learned how to make gelato in the kitchen of a gelateria in Rome and then came out and served it to the customers.  Learning how to row a gondola in Venice was also a hit.

A week is perfect for Venice & Rome; 10 days is a good length if adding on another locale.

Rome & Venice can be visited any time of year; winter is chilly, but not freezing and often sunny.  Summer is the best season to visit if you want to add on time at the beach.