Those two islands in front of Cannes are a wonderful aim for a walk. On one of them you will discover a castle in good condition. It was used as a royal prison and here was jailed the Iron Mask. On the other one, a monastery which you can visit. Both of them offer wonderful landscapes and are small enough to enable you to easily walk around them. No cars on the islands. Your children will love them. The only problem is that you have to choose before you set out. There is no boat going from one island to the other.
Going to the islands
From Cannes, the crossing to Ste Marguerite (the closest) lasts 15mn. The other one is just a little bit further. there are boats every hour or every 30mn. (Not as much for the other island. Return ticket costs 13,50€ for an adult. You can book your ticket online or buy it at the counters on the old harbour.
To St Honorat expect 16,50€ or 14€ if you buy it online.
From Nice the trip lasts one hour. Return ticket fare is 39€. There are only one or 2 boats a day. You must book your trip ahead.
That's the largest of the 2 islands. The closest from Cannes, too.
There is a fortress, as stated above. It was used as a prison and the most famous prisonner here was no doubt the Masque de Fer, the Iron mask. This man is no legend. He really existed and spent several years here and you can visit his cell. Even today, noone knows for sure who he was, and that's one of the most intriguing secret of French History. He served time during the reign of Louis XIV, the king who built the Versaille castle. Noone was allowed to see his face and to talk to him, apart from the garrison commander. He had to wear a mask (made of iron or velvet) to hide his face. The poor man died in custody in 1703 in the Bastille prison, aged around 50, having followed the commander (St Mars, a former musqueteer) each time he had a new posting. The only persons knowing the secret were Louvois, the minister in charge of the prisons, St Mars and probably the king. Until now noone found any document giving his name. The three of them probably left none.
Alexandre Dumas wrote a famous novel about him. In this novel, the Iron mask is a twin brother of the King and had to be locked in custody to keep peace in the kingdom and avoid struggles for the power. Most historians agree to say that this is only a novelist (bright) explanation.
On this island is located an abbey where priests still live. It used to be fortified and a quite impressive tower still exists, at the tip of the island. The priests produce wine and vegetables. You can even stay in the Monastery for a few nights. The abbey can be visited and you are welcome on the island. But there, you're on the priests' soil. Respect them : avoid inapropriate outfits and noise. To have fun, rather go to Ibiza...
Here you can eat in a restaurant or buy a combined ticket (19.50€) including the return trip, a panini (a kind of a warm sandwich) and half a liter of water. Anyway, you'll need much more water to spend a day there in summer.