They are meant to be 16 so it is inevitable that they look like adults dressing up as kids.
I think part of the reason I enjoy it is that I was a regular visitor to Derry in the 80's as my wife's Mum lived there at the time. Although it was grimmer and scarier than shown in the show. It is meant to be a hugely improved place to live now.
I get that, I have the same thing with Liverpool. Squiggle is right about the nun, her expressions are brilliant.