Mauritius is a volcanic island ringed by reef, with calm lagoons on most coasts and green mountains inland. Unlike the Maldives, you can leave your hotel: hike the Black River Gorges, eat dholl puri in Port Louis, visit a tea estate or climb Le Morne. The hotels are large, well run and very good with children.
Choose the coast by season. The west, around Le Morne and Flic en Flac, is sheltered and sunny in the southern winter, with sunsets over the sea. The east, around Belle Mare, has the longest beaches but catches the trade winds from June to September. The north, near Grand Baie, is livelier and more built up.
The caveats: it is a 12-hour flight, the island is busier than its neighbours, and roads between coasts are slow. Summer is hot and humid, with a risk of cyclones.