Harry Potter was a big theme at our school too. I saw more Hermiones than Harrys though.I counted 27 "Where's Wally"s at my local school (Waldo for you Amerkins). And 42 Harry Potters
In the end I found an old plain brown shirt of mine that made a pretty good adventuring tunic for a 6 year old boy, belted around the waist with a sword stuck through it and he went as his favourite character Tom from Beast Quest - which he's actually reading at the moment so it made sense too