It looks like you're in Tertenia, which I know really well! Tertenia beaches (also known as Marina Di Tertenia) are great, shallow for miles so good for kids, but not busy. I've been there many, many times. There's a fabulous restaurant up in the town of Tertenia it's called Sa Omu, and not expensive. I eat there every time I go. Also on the two beaches in Tertenia there are great places to eat, such as a simple sandwich or a fish dish at the beach bar La Duna for lunch, which is on the main big beach called Spiaggia Foxi Manna' (pronounced 'Fogi' to rhyme with splodgy!) Then on the smaller beach Foxi Murdegu ( also known as Melisenda) there's Nastasj a Mari - a bit pricey though. For cheap abundant eats try Sa Mola, bit disorganized but good food, family run, not expensive and huge portions! Hotel Janas is lovely for a romantic evening meal to watch the sun go down!
You can drive up to Arbatax for a nice evening meal in Da Lenin, booking is necessary though. You could rent a small boat from Tancau near Santa Maria Navarrese ( also nice for a place to walk around in the evening) and go to the amazing beaches of Cala Goloritzé or Cala Mariolou. We also visit Bari Sardo (pebbly & deep water) and Torre di Bari beaches, but we are a couple who stay all day on the beach! If you're self catering in Tertenia and fancy a break from cooking or restaurants, there's a butchers shop run by three sisters in Marina Di Tertenia, they do food to go such as Lasagna, Roast chickens, Sardinian pasta dishes. You can find them in a new housing area on the way to the Foxi Murdegu beach. The butcher's is called Macelleria Rosticceria Sorelle Marongiu.
A drive up to Cala di Pedra Longa in Baunei first thing in the morning gives you access to some amazing sea, climb over some rocks and then snorkeling in deep turquoise water! There's a restaurant up there to eat lunch afterwards. The sun's moved by the afternoon so has to be a morning trip to get the best of the water.
For a non beach day the Grotta su Marmuri is good.
Keep an eye out for a local 'Sagra' they are festivals usually to celebrate food-
A day trip to Orgosolo is good, bit of a trek but the murals are great. There's some great woodland walks around there too if you fancy escaping the heat such as Bosco di Santa Barbara. There's tons more I'm sure, these are the things we usually do when we go there. Have a great time!