Ooooh crikey, I could write a book on all that!! Let me try and get the best bits of info across....
Days - round the pool, canoeing on lake, walking round lake, DH tried a bit of fishing, DS played for hours in playground next to pool. Also visited some chateaux and little local historic towns - just ask at reception for their recommendations.
Temps - hot hot hot - in 2 weeks, had 1 whole day of rain & it really rained... the day was a complete washout. Were glad we were under the trees at the bottom near the pool as it kept the temps lower. Nighttime temps very pleasant & balmy.
Supermarkets - we tried the Lidls/ Aldis but then succombed to being ripped off in the large "touristy" one (sorry can't remember name) as the produce was better....
Kids club - none but every couple of days they did a morning activity like painting at reception. Your 4 year old won't need a kids club as play areas and pool/ lake are lovely.
Restaurants - only ate lunch out once I think - again, ask reception.
Journey - yes, long but very pleasant as I much prefer the toll roads being so much quieter than our UK motorways - we did an overnight both ways due to having baby & 3 year old. There's lots of different routes to get there - pick one, be happy with it and get excited as you get closer and closer to the site!!
Hope that helps.. Will post again if think of anything else or the supermarket/restaurant names come to me.