It depends on the ages of your children, what you want in terms of pools and beach access, whether you prefer a lively site or something a bit quieter, close to an airport and public transport or taking your own car. La Sirene and La Chapelle are quite popular lively sites, as is Domaine de la Yole but I've heard mixed reviews about the standard of accommodation. The Eurocamp website has pretty good filters so you can narrow down the options to meet your family's needs. Also check the parc details carefully, they state wether the pools are heated or not and they can be pretty chilly if not!
Don't be put off by the requirement for men and boys to wear tight swim shorts, it's a French law so applies to all French campsites but some enforce it more than others (it's for hygiene purposes, less likely to wear tight swim shorts as normal shorts all day/at the beach/doing sport etc. like some do with board shorts). They don't have to be Tom Daley budgie smugglers, longer style shorts and jammers are allowed and everyone else is wearing them so no one will looks twice at them!
Once you find a site you like, check out the other providers to find the best price vs level of accommodation. I've heard Roan is pretty good value, nice outdoor lounge areas and TVs which Eurocamp don't have, but we've not tried them ourselves yet so can't really comment.
Booking is now open for next summer, but Eurocamp has just merged with Roan and Homair and I think they are having teething issues with the new booking system so not all sites are listed yet but should appear in the coming weeks. Also they now have dynamic pricing so you might see crazy fluctuations in price between one day and the next. They're usually pretty good though if you ring them or use the chat to sort out any issues with pricing or answer any questions. Hope that helps!