Pondering Hard not to notice you are sitting a 45 minute paper in silence at 6 or 7.....
I agree. But that's not the same thing surely?
For DD2 in the run up they had a few sessions of doing 'special work' in silence. Children are used to doing all sorts of things that their teachers ask of them, this was just one of them. So when they did the 'real' SATs, it was just another few sessions of 'special work', no more pressure than the others.
It is a bit like the y1 phonics tests that some people get so fidgety about. Children are used to going off with adults and doing a bit of 1-1 work. No one needs to say 'this is a really important test'. They can just say 'come and do a bit of reading with me'.
So I really think that most stress on the children at y2 is due to the teachers/parents making a thing of it, and not intrinsic to the work. And if half the paper is impossible, don't they just need to say at the start 'some of this is quite difficult and we don't expect most of you to be able to do all of it, so just show us what you can do' or something like that?
Disclaimer: Unless Mrz comes back and says that due to new format / requirements keeping low key will be impossible. 
(Much harder to keep y6 low key as children are more aware by then).