I can recommend the tent linked to before, as I have the 8 person version. I know rather a lot (sdly ) about tents and this si what we chose after a lot of research (we have a canopy / footprint groundsheet and carpet for it also)
Comfort in hot weather? well first whatever tent yu get make it light coloured, dark tents heat up so badly in hot eather! If you can afford canvas how about the Khyam Indiana? Same as the last one but in a polycotton- worth a look.
Sleeping bags- cotton liners. We have a Lichfield from Argos that is cotton / flannel for just this reason.
Ice blocks- lots as most campsites do an exchange scheme. Warm wine in Italy??
for a first trip maybe a camping gaz party grill? packs down really small, built in griddle plate and burner- we have the larger version now, started with the smaller. both are excellent.
Cotton nightwear- kids want to throw off their clothes when its hot at night, but they can't nip to the loo naked, so cotton is a must!
cheapo flip flops they can wear in the showers, round the site, in streams and that you can bin instead of transporting home
try and find a crockery set that includes a chopping board / cheese knife if you want to make use of the local fare. And if you don't, ewhy not? (our Millets picnic rucksack does include this)
Drinks bottles- kids tend to forget to drink when there's no tap in front of them, well mine do- I make them carry bottles around.
My boys sleep on cheap camp beds and love them, £9.99 each in Millets. We have an airbed. If only they amde double camp beds LOL!