Maremma/Calpabio (Locanda Rossa with kids)

I would put Feniglia beach on your list, it is close to your stay. It’s the spit of land adjacent to Orbetello. Very nice natural sand beach. The other I’d do with kids is any beach you can get to in Maremma park. There is parking at marina di Albarese, but by boat you could more easily reach the others that are otherwise only reached by hiking.
Feniglia has a lot of facilities like bike rental, etc., so maybe more of what your kids will enjoy. But also with some shade for the adults! Kids will love walking around the lagoon at Orbetello and there’s great gelato of course!
I’d also check to see if any wildlife events or activities are on in maremma park. This tv show featured the park: https://www.peacocktv.com/watch-online/tv/earth-odyssey-with-dylan-dreyer/8608785637761706112/seasons/8/episodes/wild-tuscany-predators-and-prey-episode-7/a264c083-d1c3-3d95-aec7-6423fb7f8367
We saw a fox on the beach last time as well.
If they don’t get car sick, drive around Monte Argentario and check out the views.
Last, be sure to check out some vie cave, kids will love those!

I don’t know when you are going but in summer there are beach clubs at the following locations, which are not far from the Locanda Rossa. I don’t know if any of those clubs rent pedalò (pedal boats) or pattini (paddle boats). But all will have sand, and umbrella and chez for rent.

Ansedonia: https://maps.app.goo.gl/YdWTu9TeJP1FJnWw8?g_st=ic
Feniglia: https://maps.app.goo.gl/upPHTWkQHNbu1Xmx7?g_st=ic
La Giannella: https://maps.app.goo.gl/iXNp6jtpcnQVKZQY6?g_st=ic

I’ve been to the last two and I saw some pattini.
Generally when I go to Mt. Argentario (I stay at Porto Santo Stefano) I like to go to Giglio. No need to charter boats, that would be expensive. Just drive to the location below, park in the parking lot (maybe 15€ for the day), buy the ferry ticket, cross the street and take the ferry. Ferries are frequent and you could even take the car, but in summer you need to reserve in advance, and certain periods only the Giglio residents or hotel guests in the island can take the car. The ferry ride is less than one hour.
https://maps.app.goo.gl/bX9n15s2cRBLkUSk7?g_st=ic
Once in the island there is a city bus from Giglio Porto that goes up to Giglio Castello then descends down to Campese. Castello on top is a quaint fortified village with great views but probably your kids don’t care, as kids like beaches. If you don’t plan to go up, near Giglio Porto I like to go to the beach below called Spiaggia delle Cannelle. It is a gorgeous beach and you can rent umbrellas and chez. Don’t remember if they have boats for rent, but it’s worth going to the island one day. You can walk to the beach, but it’s a longish walk, so usually my wife and I walk to it, but then take the shuttle bus back to Giglio Porto. It’s a 5 min ride on the shuttle bus.
https://maps.app.goo.gl/rVQer9AxcXkckCrT7?g_st=ic

When you come back to Porto Santo Stefano, next to where you parked and next to the ticket office where you bought the ferry tickets there is a good fish restaurant. I think it’s called “Il Veliero” now. It’s good, but it’s very busy so you might want to book before you go to the island. Sometimes they still accommodate me even if booked if I promise to be done eating by 9:30pm (Italians eat late so they come at that time). If you don’t mind to walk a little from there you can also try the Trattoria Lo Sfizio 2. A bit more expensive but even better. There is also the Trattoria Dai Frati that is good. But in that case you might want to drive to it, as it is up the road and it would be too long to walk. You can see where they are on GoogleMaps.

Great!! Thanks so much for all of these recs! We will try those beaches! Next question: any restaurants we must try? Again, we have 4 kids ages 7-13. They are well behaved and are used to dining out. Any farm to table recs with animals on property? They love that!

The Locanda Rossa, where you are staying, has a restaurant that is highly rated and fancy. I doubt they have animals roaming around, though. However, I checked their menu, and it is very expensive by Italian standards, like California prices. Not surprising. The village of Capalbio is the refuge of the Roman elite (politicians and show business VIPs), so you pay accordingly. It’s like going to Martha’s Vineyard and hoping to get low prices.

About 10 min from your location I found this agriturismo that is highly rated by Italians. Prices are half of what they have at Locanda Rossa, and it is probably more authentic and traditional.
https://maps.app.goo.gl/kkAtYqiFn8Md4GxK7?g_st=ic

In the village of Capalbio itself, I think I ate at the restaurant below. But I don’t remember for sure, it’s been 4 years.
https://maps.app.goo.gl/wyHpCVfDCG7GNASb9?g_st=ic

In the Island, at Giglio Porto I like this restaurant. I had lunch here. Not sure you can go to dinner if you plan to take the ferry back to Porto Santo Stefano, as ferries stop operating at a certain time in the evening.
https://maps.app.goo.gl/whxo1wooVPWWqgxU6?g_st=ic

If you tell us where you intend to visit while there I can give you some more suggestions. Nice towns to visit in the area are, besides the places we mentioned above, also Massa Marittima, Talamone, Saturnia, Pitigliano, Orbetello. But I don’t know if you plan to just stay at the beach.

Thanks for your detailed responses! Thoe restaurants look lovely! We plan beach days but are also open to visiting other towns- out of the ones you mentioned is there one you would choose over the other? My kids love outdoor activities so anything active would be great.

There just isn't much on forums on Maremma-- maybe it's not as popular for tourists? Or at least people from USA

I always wanted to see the Tarot Garden near Capalbio but missed it on both trips.
There is a WWF refuge north of Orbetello with flamingos—seasonally dependent and requiring reservations.
I like Pitigliano, it’s got a dramatic approach. There are many vie cave in its vicinity that you can walk through, with additional Etruscan ruins at the site near Sovana. There is some kind of archaeological/historical park right outside Pitigliano that might be fun for kids.
And of course the hot springs at Saturnia, but we found that disappointing, as I’m not one to share spa time with hundreds of others, lol.
Try googling the blog posts of food writer Emiko Davies, who lived in the area and has children. She mentioned some farm restaurants on and near Monte Argentario.

Massa Marittima and Pitigliano are probably the top most visited towns of the list I made.
Grosseto, the Province’s capital city is also worthwhile. It’s a city, not a small village, but it’s the only city, together with Lucca, that still has intact city walls all around. Saturnia has the famous natural thermal spa at the Cascata del Mulino . They all require some driving time to get to them.
Near your accommodations there is also the Parco dei Tarocchi (Tarot Park) which your kids might enjoy.

Maremma is a part of Tuscany that is not at all well known to North Americans, but I think it is one of the most beautiful rural areas of Tuscany. It also has the best coast of Tuscany. It is popular with Europeans though. You can find info resources in the area official website below
https://www.tuttomaremma.com/en/

I will look at blogs from Emiko Davies- sounds like I can get more insight there too. I will also look into Massa Marittima and Pitigliano!

I really appreciate you all taking the time to respond about this leg of our trip. To be really honest I'm a bit nervous- our travel agent recommend Maremma and I know nothing about the area; I just want to make sure it's magical for our family. My first pla was Amalfi but that's too far and I think too hard with 4 young kids. We went to Mallorca last year and just had the most magical time staying on a farm and going to the beautiful beaches- I want to recreate that "magic" of the countryside and the sea! I keep questioning myself and wondering Venice, Tuscany, and Maremma is what I'm envisioning for us! But again, I question everything I do! lol

This is my favorite part of Italy after about a dozen visits all over the country. I don’t think you will be disappointed at all. I have not been to Mallorca, but if you like nature and rural travel, you will be absolutely pleased with this area. It can be buggy, but that is the only criticism I can muster. And it’s not just nature, as there are pretty hill towns and archaeological sites scattered throughout. If you make it as far north as Piombino, the park at Baratti is great, too, but you’ll have plenty to keep you busy in the immediate vicinity. The only reason it’s off the radar is that Italy is just stuffed to the gills with great places. FWIW, I’d never take kids that small to the Amalfi coast to deal with those crowds and costs, plenty of worthwhile alternatives exist!

That is so great to hear! I do think we're making the right choice! Best, Alyson