I'm always hesitant buying a costume online.  I ordered this Batman costume for my 4 year old son who had to be the black Batman.  He wears a size 5/6 and crossed my fingers that the costume would fit him.  It fit him perfectly.  The only problem fit wise is the cape.  It attaches with Velcro around his neck and it is pretty tight.  The cape is also very long.  The mask is hard plastic with foam around the eyes, so it is pretty comfortable.  This costume has been worn quite a bit and washed a bunch of times, so far it's holding up great.