Coastal Cities in italy

Sounds like the Amalfi coast would be perfect for them. Stopover in Rome for a night upon arrival then train down to Naples.

If you are looking for Florida like beaches, Italy has very little. If pebbly beaches are acceptable your choices are more plentiful.

What kind of waterfront do you need?

The beaches in Italy are not memorable.
What is nice are the scenic coastal areas like Venice, Sorrento, Capri and the Amalfi Coast. Also, Cinque Terre.

Croatia is great, especially Split and Dubrovnik.

On west coast, north of Rome, many nice towns with beaches.
Capri and the Amalfi Coast do not offer comparable beaches.
At beaches, you often rent sun beds.
Look at the Portofino Peninsula with the lovely towns of Santa Margherita Ligure and Camogli.
Cinque Terre- Monterosso has a small sand beach.
Portovenere- sand beaches
Forte dei Marmi- nice beaches, more upscale
Ventimiglia-nice beaches

Memorable beaches in Italy are plenty but few Americans have ever visited those localities, including many in this forum, because they are not near the typical destinations Americans go to.

The Ligurian coast (Cinque Terre), a popular destination also for Americans, has jaw dropping coastal views, but it is a very mountainous region, with mountains dropping into the sea, therefore what you have is a lot of cliffs, with small pebbly coves and beaches, but not really sandy beaches.

The exact same is true for the Amalfi Coast, Capri, and much of the Campania coast (Naples area). That coast is super beautiful, but very cliffy, so at most you get some nice small pebbly beach, but no white sand beaches.

If you are looking for memorable beaches, with great sandy beaches, you would need to venture off the American tourist beaten path.

Sardinia has some of the best in the world, not just the Med:
https://www.blualghero-sardinia.com/en/10-stunning-beaches-in-sardinia-make-you-think-the-caribbean/

Sicily has a few also. The most famous beach is at San Vito Lo Capo, western Sicily.
https://images.app.goo.gl/LNG3fVgyJQgYGxFt7
But Americans who visit Sicily, generally prefer to visit the cities and the Greek ruins, not the nice beaches that aren’t so easy to reach.

Puglia has beautiful beaches too, in particular on the Salento Coast or the Gargano Peninsula (which however is kind of cliffy too)
http://www.stayciao.com/blog/3-must-see-beaches-in-puglia-salento/
https://www.beautifulpuglia.com/top-10-beaches-gargano/

The smaller Italian islands (Tuscan Archipelago, Ponziane islands, Gulf of Naples islands, Eolie islands, Egadi islands, Tremiti islands) have great places too, but they are not easy to reach, and many are cliffy.

You will not find memorable beaches near Venice or near Rome, or near Florence in Northern Tuscany (Versilia), but those are the ones most Americans have seen since they are easy to drop by from the aforementioned top destination cities.

There are some nice beaches in Ischia, but it’s an island, drawback is it’s an hour by ferry from Napoli, if museums & sites are your interest. Very cute towns, excellent food, great place to hike
More of a laid back area once out of the Porto area.

https://www.ischiareview.com/beaches-of-ischia.html

I love Treiste which is on the Adriatic coast. We stayed here on the RS Southern Italy tour and I loved this city. It was big enough to have something to do at night but not very touristy (at least with Americans...I hear Germans love this get-a-way city).

To pair with Croatia ; Bari could be a good choice. Likely makes connections easier/shorter being so close and there is plenty to do in that are if you rent a car. From the coastline to Matera.

Or Naples as others suggested for the Amalfi Coast/Sorrento area

I love Italia, but I think Croatia has a bit better beaches - if you prefer sandy beaches. But like others have said, Amalfi Coast is nice if you want to be by the water - then you'll be close to places like Napoli, Pompeii, and Capri that are all nice to explore (and Naples has best pizza).

Would also suggest Cinque Terre - most of the sandy beaches are in Monterosso al Mare, but there are still other nice rocky beaches, and the five villages are very close together and easy to reach with the Cinque Terre express train. But you want to avoid cinque terre during peak season because lots of cruise shops stop by nearby La Spezia, and then the towns get crowded.

Sicily is also very good for beaches if you're okay with going more south. We always use this local company Isula Travel to find places to stay there on our holidays, but I know they do Croatia places too - https://www.isulatravel.com/villas-croatia/villas-croatia-private-pool

Still think Croatia is a very good option, especially for a family trip. The beaches are very beautiful, and Croatia can be a bit cheaper than Italy.

Hope that helps :)

You might be hard pressed to secure accommodations for this June in the Amalfi Coast--it seems to have exploded in popularity, and it was already popular. Just to the south is the Cilento coast, which has marvelous sandy beaches and some picturesque pebbly coves reminiscent of what you find in Croatia. Pretty hill towns, too.
Puglia also has many fine beaches, especially north of Gallipoli, plus some great sites to see for those who get bored with beach time.
My favorite beaches have been in southern Tuscany (the Maremma coast has wild natural sandy beaches, Monte Argentario has rocky beaches that somewhat remind me of the Amalfi Coast) and on the Adriatic in Marche near Ancona--the Monte Conero area (Sirolo, Numana). Coincidentally, those beaches also remind me of Croatia's pebbly beaches with clear seas.

Of course you should also consider Sardinia, long a dream of mine as a coast lover.