We are just back from 4 days Sorrento - adult only though
We did 1 day Pompeji, there is a direct train from Sorrento, it was €12 return for both of us, it's very popular and often standing room only.
Pompeji is a full day, we had the tickets incl. the Villa of Mystery and spent 6 hours with 1/2 hour sit down for lunch. We skipped the amphitheatre.
Not all houses are open all the time, some were closed for work as well. It's a lot of walking and while the audio guide is good, it depends how good your general knowledge is, there were plenty of groups, some walking fast, basically just doing the big ones with 20 people and headsets while you had smaller/private groups who were a lot more in-depth and happy to go how the tourist wanted.
There is a cafe in the middle, decent food and drinks but obviously expensive. There is not really anywhere to sit otherwise.
Herculaneum - around 1/2 the size. I found it better going there after Pompeji and there is more to see as the houses are more intact. I think we were there for 3.5 hours. The audio guide is a nightmare though, it often breaks down and you have to start again. The layout is also a bit more confusing but after a while you get the grip.
There is a "food court" but that's vending machines only.
While you can go by public transport, we had the car and there is a car park next to it for €2/hour.
If you are unlucky and it rains, take waterproofs and umbrella.
We arrived with 25 degrees, had one afternoon of rain with 16/17 degrees and the rest a mix of clouds/sun around 20. Jumper and coat is definitely needed for the evenings.
Sorrento is nice, very touristic and crowded. Food is not cheap though.