Can you try on nightwear (PJ's) in the shops changing rooms?

Hi. I'm getting some new pyjamas from peas. they the new bottoms with the rolled up hem and im getting a t-shirt which is separate. as anyone who stops there will know not all sizes are right, they're small or too big like a size10 is more like size 8 or 12, and as i'm paying �12 for the pair i want to sure they will not be too baggy/small and fit great but im not to sure if you can try them on?