Hi,
Winslow and I are in Massachusetts, I do not cut his coat for the summer, you just need to rake it frequently, I would assume (and you know what they say of assuming) that your climate is fairly close to mine. Meaning a longer cold winter then hot summer. The coat is an insulator, meaning it keeps heat (winter)or cool (summer) in when needed. Your puppers metabolism will slow down when it is hot, just like your's I bet!! If you feel like jumping in a pool or the lake you can be sure your Newf does too, if you are not as hungry because it is hot, pretty much the same for the puppers!!
Their skin is white so a short coat can lead to sunburning the skin,meaning more dandruff and scratching (like when we get sun burnt) the breed has survived a long time in varying climates so you really don't have to mess with the coats you just have to care for them.
I say if you feel hot they probsbly do to. If you want to sit in the airconditioned house bet they do too!!
The kiddey pool is fabulous!! get one for each and change the water daily your pups will use it when they need too, and often just because they want to.
So I guess my point is, if you are feeling uncmfortable with the heat, what do you do to cool off, in all likely hood you puppers will be feeling exactly the same!!
Hope that helps!!