Arborea is perhaps the closest beach from our B&B (25 minutes by car). It is a very long beach, so you will always find a lot of space. It is also the easiest to reach, since the path is almost straight.
It is perfect for children because of the shallow water (very warm in the summer), and fine-grain sand. Moreover, there is a wide pine forest, that can be freely accessed for picnics and car parking is free.
In Arborea you can also book horse riding tours, that go through the sea, beach and pine forest, for an amazing experience.