In reply to Bob Kemp:
July and August in sunbathing holiday spots are going to be crowded wherever you go, but consider the Ardeche for a location which gives your family water to play in and climbing / bouldering for you. Many of the rock climbing sites are polished but if you start from the point of finding somewhere that is fantastic for kids to play and non climbers to roast on the water's edge, you can find plenty of rock for yourself and lots of people to climb with if you stay on or near a camp site. Early morning cragging is particularly beautiful and then join up with the family for some splashing around fun. Check out the area around Chaulet Plage on the Chassezac rather than anywhere near the Pont d'Arc.
I went to Sardinia in early July last year. It is a lovely place, but to climb in the shade you will drive many miles on winding roads in frustrating heat and as someone else said, the night time sleeping (or not sleeping) temperatures require air con. We lasted two nights in a tent before renting an expensive apartment.