Hello! We are a family of four getting ready for six night stay in Rome in April 2019. We arrive to FCO on April 13 around noonish and depart on April 19 (good friday). We are staying in an apartment in Trastavere (Viccolo del Cedro is the street). We intend to travel light and would prefer using only public transportation. I just bought a guidebook

There seems to be trains and buses from FCO to Trastavere - what are the options? Should we be looking at some kind of pass? Boys will be 5 and 8.

Any advice would be greatly appreciated! Thank you from Boston.

It's been a few years since I was there, but the Rome integrated transport ticket was available at most metro and railway stations, and allows you unlimited transport within Rome by train, bus, tram and metro.
I think it now costs about €24 for the week (The 72 hour pass is €18 - so you'd be better off with the weekly ticket).