Luggage storage at Pompeii

There are no lockers, just a secure luggage storage at the station. It’s located downstairs under the track.

Luggage is not allowed inside of Pompeii (no bags larger than 30 x 30 x 15 cm). If you are traveling with luggage, you can store your luggage in the luggage storage facility (deposito bagagli) in the lower level of the Pompeii Scavi station. The cost is €8 per bag.Jun 15, 2022

I have not used the Pompeii Porta Marina luggage storage, but many people, over may years, have given good reports of it here. Do you understand that the Porta Marina entrance to the ancient site is only about 300' from the Circumvesuviana station we are talking about. (Note: You did not say "Circumvesuviana", so we need to know that you are not talking about the Trenitalia stations in "modern" Pompeii City.)

You may wish to use the good Search function here (blue menu top left or center) to get some idea of how much time you will want to spend inside Pompeii, food, sun and heat, and so on.

Yes, the Scavi station does have luggage storage. However, you may be more comfortable continuing to Sorrento, checking in at your accommodation, and then heading back to Scavi (either the same day or another day)? The station is right in the middle of Sorrento so unless you are staying up in the hills you can easily walk back and forth. I've been to Pompeii twice and going the first thing in the morning is best because it gets hot and crowded. Either way, I suggest you ask for a map at the gate (they don't just hand them out) and you may want to download Rick's walking tour, the signs are in Italian and there are no directions.

Here are some other tips:
The Circumvesuviana line from Naples to Sorrento is a local train with no AC (beware the gypsies and thieves, keep your bags close). The views of the bay and the mountain are great.
Don't get on the wrong train in Naples you want the one going to Pompeii Scavi...not Pompeii.
Bring a water bottle, you can fill it inside Pompeii. There are very few food options so plan for lunch back in Sorrento. The fresh lemon "snow" near the entrance of Pompeii was expensive but great on a hot day.

Herculaneum "Ercolano Scavi" is on the same train line and is also easy to get to, you can even do both in the same day.
Il Bufolito (little buffalo) in Sorrento is a great restaurant, you may need a reservation for dinner.
The beaches in Sorrento are not great for swimming and the walk back up at the end of the day is brutal.
Take a shared charter tour of Capri if you have the time it is wonderful (instead of the ferry). Pick one that goes all the way around with a lunch stop in Marina Picola, you should have time to get lunch and then take a taxi to the top of the town for some expensive luxury shopping or some gelato and views. A stop at the Blue Grotto is also lovely but you'll have to switch to a dingy to get inside, your tour operator will arrange it for you. Tours/ferries from October through spring often get canceled because of high winds.
Picnicking in Sorrento is easy there are several little grocery stores to grab what you need for the day.

Don't get on the wrong train in Naples you want the one going to
Pompeii Scavi...not Pompeii.

Hi Donna, welcome to the RS forums -

Actually, all you need to do is get on the Circumvesuviana to Sorrento: Sorrento is the end of that line, and the train stops at Pompei Scavi - Villa dei Misteri station, which is along the way, on virtually every run it makes. Same for its runs from Sorrento> Napoli. Here's the current schedule:

https://www.sorrentoinsider.com/en/naples-to-sorrento-train-schedule

If you're coming into Napoli Centrale from Rome on a "fast" train, you'll change to the humble Circumvesuviana commuter train at Napoli Garibaldi, which is connected to Centrale, You don't even have to walk outside to go from one to the other. if you decide to go to Sorrento first and then backtrack to Pompeii, just use the toggle feature on the schedule to reverse the route.

You could also opt to hire a private driver to Pompeii and then take the Circ. on to Sorrento, or a driver to who will cover the entire route. Obviously it's more expensive than the commuter train but some folks like to go with that method.

I'll also kindly disagree with trying to do BOTH Pompeii Scavi and Herculaneum on the same day, especially if you will be traveling during the summer months. When is your trip?

The OP didn't propose going to both excavations in one day. But since Herculaneum is 15 steep downhill minutes from the Circumvesuviana (no storage at unattended station), I wouldn't do that with luggage anyway. No food inside Herculaneum, either.

Depending on budget and family sentiments, you could also be guided by weather. If the day is clear and cool, that's a good day to see Pompeii. I consider 3 hours insufficient, but you know your family's level of interest. It is entirely fair to say you "saw Pompeii" in three hours. But it's big enough to fill eight hours or more. You may also be thinking of the whole week's weather forecasts for other excursions, since transit connections likely figure in your decision to stay in Sorrento. (We spent five nights in Sorrento, one night in Naples, that one related to air schedules.)

We stored our carryon sized luggage in lockers next to the Pompeii entrance instead of at the train station. The lockers were free and large enough. We did encounter several people between the station and the site who offered to store our bags elsewhere, but ignored them and continued to the official, free storage instead.

The OP didn't propose going to both excavations in one day

No, they didn't. It was a responder that said that Herculaneum was, "....also easy to get to, you can even do both in the same day."

Thank you all so much for you help!