Pompeii and Positano in 1 day

If you are staying two hours away from Pompeii you have already lost two hours in the day driving there. Then, spending any less than half a day in Pompeii would be a waste of time and money spent seeing the ruins. Add to that the driving time to Sorrento, ferry time to Positano or Capri, plus driving time back to your place of residence, and I can't see that you would have any time left to enjoy a beach if you could find one. Driving to Positano is harrowing and not for the faint-hearted. I would not recommend doing both places in one day. Better you spend the day in Sorrento after you leave Pompeii.

I would be happy to spend the time in Pompeii. Though Sorrento is not far away, in off season,

about a 45m drive. If you are going in the summer months, this short stretch could take 2 hrs.

This will give you an idea of the "Beaches" http://www.positano.com/en/beaches .

If you still have time after Pompeii, you might stop in Caserta which is on your way back to Anagni.
your girls may forgive the no beach.

http://www.realcasadiborbone.it/es/dinastia-2/palacios-y-residencias/el-palacio-real-de-caserta/

I believe u are trying to squeeze too many sights that r too far from one another to enjoy. Pompeii can take half a day to see and enjoy alone. Positano while a wonderful place to see is too far to see and do from Pompeii. And if u do decide it has a very small beach. It is mostly a steep hilly village for shopping boutiques and staying in gorgeous hotel spas and dining with lovely views of the Mediterranean.
Capri is an island that usual takes 1 day for rd trip ferry and walkabout of the island. Perhaps u could prioritize and just do one. The visit to Positano should be fine by public bus or by ferry.mthere is no where to,park your car unless u a staying at a hotel there. Also the Amalfi rd is treacherous. I am used to our coastal rd hi way 1 here in California, and it pales in comparison.
Hope this helps a little.

What time of year? Will it even be beach season?

There are, I believe, beaches at Vico Equense and Massa Lubrense, although I have no personal experience on them. Could you go to one of those, which are close to Sorrento, and spend one night either before or after Pompeii? Then you can have a beach day and a day at Pompeii.

Pompeii and Positano are in opposite directions. Laurel's suggestion is good. Beaches in the area are mostly rocky/pebbly. There is a small beach at Amalfi town.

Thank you for your advice, even though it's disappointing. On our 2 week trip, in July, we are spending 1 week seeing Venice, Florence,and Rome. The 2nd week we are visiting family we only see every 10 years or so. That's why I was trying to pack as much into our day trip away as possible. We've never been to Pompeii, the Amalfi Coast or Capri, all of which have always been on my wish list. I have seen guided tours advertised that go to Pompeii and Positano in one day, so I was hoping to do the same on our own.

Visiting Pompeii in July can be hot and exhausting. Try to get there as early in the morning as you can. And still budget about 3 hours there: 2 hrs for a guided tour (tour guides are very affordable and available for hire at the entrance) plus 1 hr to walk around on your own.

Afterwards, your girls would definitely enjoy some beach time. But I wouldn't try to do the drive all the way to Positano. The ferry to Capri would take too much time as well. Find a beach in the vicinity of Sorrento. This website gives you some options:
http://www.destination360.com/europe/italy/sorrento/beaches

We have a private tour lined up with Simply Amalfi this summer from Naples. We will drive the peninsula via Sorrento in the morning, with plenty of time in several villages, then tackle Pompeii in the afternoon, about 8 hours of touring. It will be brutally hot in July, but doing it the opposite order from all the big cruise ship tours should help us avoid crowds. We have toured this area twice before, once with a large tour group (wasted too much time in a stupid restaurant), but took a boat up the coast. Our second time, we spent all day on the coast. The views from the sea are lovely, but nothing compared to the views from above! I highly recommend a private tour rather than driving that crazy road. Could you take a train and meet a driver?

I know that some will think I am crazy, but if I had to choose, I would take the coast over the ruin any day to spend most of my time. It is some of the world's most beautiful scenery! I love Positano, Amalfi and Ravello. Teens would probably not be too excited for 3 or 4 hours in Pompeii when it is so hot. You might want to consider a shorter tour for their sake. Check to see what time the earliest and latest 2 hour tours of Pompeii are and plan accordingly. Bon voyage!

Jan

No way. We just got back from southern Italy, staying in Salerno. With NO tourists/traffic, it took an hour from Salerno to Amalfi by bus, and it would have been another hour to Positano. For Pompei, we took the Trenitalia and spent 4 hours in 60 degree weather, without crowds, seeing the ruins, and could have spent 6 hours easy--it's that good, although in July I might end up like one of those guys lying down there... :)

As stated above, unfortunately I think you need to winnow down your sights somewhat. If the girls like the beach, go to the beach. Good luck.