My 11 wanted this for the school disco. As he is not the biggest child, I was a bit nervous about sizing but it was perfect. He tends to wear 10-11 yr clothes rather than 11-12. He's skinny too. It didn't ride down though he still had a bit more room to grow. If you have a larger/taller 11 year old, you might find this a little on the small side.
Well made, I was expecting stocking like material but it is thicker than that.
Only problem for him was the mask section. He has such very long eyelashes that it was awkward to blink. After a short time he did let the head piece hand down at the front cos it does get hot in there too!