Europe with a 3 year old! Oh my! As to using the train from Rome to Civitavecchia, I imagine most children would love a train ride (they either sleep or look out the window). Once you get to Civitavecchia it is about a 4 block walk to the port entrance where you can get free bus shuttle service to your ship. If you can handle the luggage, it is actually a nice walk. You can cross the street and walk along the seaside and there is even a McDonalds right before the port entrance which makes many 3 year olds smile.