We took our grandson and baby sister to Italy for two weeks a year ago --- he had his 4th birthday there.
We were not in Milan with him but he would have loved the top of the Duomo, the old-fashioned street-cars, and the huge Galleria Vittorio Emanuele II. He would have loved the monumental cemetery too, but would have been way too noisy and wild there.
He and his sister were genuinely welcomed in every restaurant, even for dinner. The servers were impressed with how much he ate and what foods he relished, like prosciutto and other preserved meats. His parents were always nervous that he would act up, especially during some very long lunches, but he never did. We had all kinds of quiet things to do with him, like we drew mazes in a notebook. Or one of us would take him outside to walk around and look at stuff. Choose your restaurants wisely and your kids will be fine. They might need to be kept quieter than in many American restaurants.
In general, he was intensely interested in how things are different in Italy and to this day asks us how to say something in Italian and whether Italians do such-and-such of a thing unlike Americans. He was constantly discovering. He was enchanted by how the toilets flushed and how the water in the sink got turned on with a foot pedal in some restaurants. How the windows opened. The three-wheeled little truck called an Ape (AH-pay) which he spotted everywhere and became an expert on. He could hardly believe his luck whenever he could run around in a car-free piazza or watch the older kids ride bikes or play soccer. Gelato, of course. Bakeries. Ordinary Italian life seemed to be enough --- no need to do too many things especially for kids.