we went when dd was 1, am racking brain:
buy or borrow the angela bird guide
make sure your satnav has up to date fr maps and program in the location of the site using the coordinates (N 46°39'39" W 1°42'56") not postcode
take bikes if you have them, also scooter for ds1 to whizz round site
the best supermarket is the big Leclerc complex at Olonne-sur-Mer
the best beach we found was Paree-Plage at Bretignolles - couple of restaurants and cafes round a little piazza, lots of sand, also rockpools and not too busy
take a kite
and the big (ie not maclaren) pushchair if you have the room
make sure crocs / sandals are named as you have to leave them in pigeonholes by the pool
make sure you request your free baby kit (highchair, nappy mat etc) from rep on site
this thread is good