The Beau Rivage Palace in Lausanne, complete with indoor/outdoor pool AND a giant chess board on the grounds. Get your money ready.

Lac annecy!

Lake swimming is cold in that area! But Annecy is nice, even though you have to stay away from areas with ducks, because apparently "duck lice" are a real problem.

Thanks! Good to know about the lakes being cold!!

Divonne-les-Bains near Geneva :
www.divonnelesbains.com -

You don't need to leave Geneva. Go to the jetty which sticks out from Quai du Mont Blanc. Lac Leman is the sweetest water I have ever been in. The lake is not cold in the summer. For me it was perfect swimming temperature. It has lockers (bring coins) and a pleasant cafe. If the weather is right you will have a beautiful view of Mont Blanc, 50 miles away across the lake.

Yes in Montreux (which is a French-speaking area) you can swim right in Lac Leman. There's no beach but people go in off docks, piers, and the rocks.

The Casino hotel in Montreux has a fabulous pool area (it's very near the lake, tucked in just the other side of the quai - lakeside promonade) that you can buy day passes to.

There are also some cool public/civic pools in the area.

http://www.montreuxriviera.com/en/page.cfm/culture_leisure/Sports_ete/Sports_aquatiques_F/piscine_plage

The pool at Clarens (first on the link above) is a large public one with both indoor & outdoor pools. Also grass park area for picnics. If you want to be among locals, this is the place. I think it would make a great stop and activity for kids that age (definitely French-speaking). There's lockers you pay to rent, showers, etc.

It's the year of water for the Swiss Tourist Board, so they have a lot of suggestions on their site http://www.myswitzerland.com/en/summervacations.html and you can order a brochure about accommodation by the water. They publish current water temperatures on their site and iPhone app in the summer too.

There's a wee public beach at Estavayer-Le-Lac with good swimming, and other stuff for the kids around, and there's excellent swimming plus mountain walks at Schwarzsee, just east of Fribourg. Excellent outdoor pools everywher in the summer, we like Chexbres near Vevey and Chateau d'Oex is supposed to be great.

There are beaches and swwimming at the Lac de Joux in the Jura too, about an hour from Geneva.