Is Pompeii a day trip from Rome?

It is possible, but not recommended, to visit Pompeii as a day trip from Rome. You have to change trains in Naples and it takes about 3 hours each way, not counting getting yourselves to the station in Rome. The time spent traveling means you won't have much time at the scavi in Pompeii.

The town of Pompeii has hotels and B&Bs as well as restaurants, so an overnight stay is easy to arrange. If you're searching on a booking site, you may want to enter "Pompeii Archaeological Park, Pompei, Campania" as the location. There are places to stay within less than 1/2 mile of the scavi.

With only 8 days in Italy, clearly you'll have to set your priorities and know that you're just scratching the surface. Since Pompeii is important to your son, you may want to shorten your time in Venice to do justice to a Pompeii visit.

What is your destination after Rome?

We were thinking of doing Rome Pompeii and Venice in the 8 days. Do you think this is doable?

Venice is our final destination.

Rome//Pompeii/Venice by train in 8 days is certainly doable, but the Rome/Pompeii travel part will require a good part of a day. Staying in Pompei (modern city) after visiting Pompeii (ruins of ancient city that was buried by the volcano) would let you start off for Venice from there. Staying in, and visiting Naples, would allow you to see the amazing National Anthropology Museum, where most of Pompeii’s recovered artifacts actually have wound up.

Your son may not be interested, but just outside Rome, to the southwest, are the fascinating ruins of Ostia Antica. Ostia was the port of Ancient Rome. Rather than a volcano, it got buried over time by silt, which preserved building walls, structures, mosaics, even a remarkable ancient public mass toilet facility. Closer to Rome, similar sights, maybe not as famous, but Ostia Antica’s worth considering.

Can you arrange your flights to make Venice-Naples your entry-exit points and thus eliminate back tracking ?

Otherwise I would suggest Ostia Antica as your 'ancient Roman city' experience and spend more time being someplace rather than 'en-route' so much in the limited time you have

An high speed train from Roma Termini to Napoli Centrale takes 1 hour and 12 minutes.

10 minutes to get off the high speed train and walk to the underground tracks at Napoli Centrale.

The Circumvesuviana trains to Pompei Scavi take between 35 and 50 minutes. The Campania Express is faster, 30 minutes to Pompei Scavi.

So it's around 2 hours if you pick carefully the departure hour from Rome. 4 hours return... departing from Rome at 7 AM... I'd rather visit Ostia Antica, but it's definitely doable.

https://community.ricksteves.com/travel-forum/italy/pompeii-day-trip-from-rome-2c38f926-9036-480d-95fd-403dd7694e4a

Be aware that Pompeii can be very sunny and oppressively hot, even in May. That doesn't take away from the value of the visit; I'm just suggesting that you plan carefully to conserve your energy. Many people spend six or more hours at Pompeii. Allow time for lunch, inside the site.

I say no, there is a lot more to see in the Bay of Naples area.
Sorrento, Capri, the Amalfi Coast as well as Pompeii.

Can he go to Pompeii on his own while you continue your very short visit to Rome?

It sounds like you have already arranged to fly into Rome and out of Venice?

our hotel in Pompei.

You are staying in modern Pompei? Did you virtually walk around your hotel with GMap's StreetView?

I have been to Pompeii twice. The first time was a day trip from Rome and it was really great. We took an early Italo train from Termini Station to Napoli Centrale and chenged to the Circumvesuviana line for the final leg to Pompeii. We spent 5 or 6 hours at the site before making our way back to Naples. We even had time to visit an amazing pizza place in Naples before catching our train back to Rome. It was a long day but it was really a wonderful experience. The other time I went to Pompeii was also a day trip but this time from Sorrento. The train trip was much shorter but we still only spent 5-6 hours at the site. We were back in Sorrento before dark which was nice but I really wouldn't rate one experience over the other. For me, 6 hours is about all I can handle at a site. If you can stand 10-12 hours you would probably be better served staying closer. I always assume I will return one day so I don't try to see everything in one visit. Good luck with whatever you decide.

Just to add, realize that the ancient Pompeii is/was an entire city. When people talk about spending 5-6 hours there, they're not exaggerating. There is something to see in every building on every street, not to mention the Villa of Mysteries and other outlying buildings.

We did a tour of Pompeii and Amalfi coast in a day we left Rome around 7am and returned around 8pm it was a very long day but one of my favorite memories of the trip. We used Walks of Italy perhaps that would be an option if you don’t want to stay overnight.