I have not been to Sardinia but we did a trip to Sorrento and Rome for a total of 1 week when our children were 1.5 and 3.5. Rome is a very walkable city and ours did fine in a double wide Mountain Buggy. While apartments can be nice, we have had a nightmare with one in our travels and we tend to stay in hotels with connecting rooms or apartments within the hotel. So the apartment is not a MUST in my opinion. My children LOVED the fountains in Rome.

We went in January and found Sorrento to be practically shut down. The original plan was 1 week in Sorrento but we left after 3 days. Literally there were about 5 restaurants open in the entire old town. So, if you are going in March, you may want to consider the season. Again, I know nothing about Sardinia.

Rome was such a great winter destination we are going again this year.