You can dangle a fishing rod in most places and it's often something you can do by yourself from a harbour wall, from the beach or from a boat.
To enjoy a day out on a family fishing trip then we recommend speaking to some of the specialist companies who offer guided trips and excursions or yacht charters for coastal or deep sea fishing. You have a few options for fishing charters with a range of budgets, from 50 euro per person for a casual affair to 2800 for 10 people for the day for the charter of a luxury sports fisher with professional fishermen. Most of the fishing excursions along this stretch of coast operate out of Golfe Juan or Mandelieu-la-Napoule, near Cannes. If you charter the entire boat then they will pick you up in Saint Tropez.
Around the ports of Saint-Tropez, Grimaud and Sainte-Maxime there may be some small local operators who don't have websites - you'll see signs saying 'Peche au Gros' in the port and you can enquire with them directly.