I thought I'd share this, as having to buy trousers for skinny boys is such a nightmare!
Ds has recently grown, but only in height... We went to Gap, tried a couple of pairs of jeans and they were all ridiculously baggy.
I left him in the changing room to get some more and picked up a pair of straight girls jeans in his age and height size, and they fit him like a glove!
The label inside thankfully says "child jeans", so he is not embarrassed and I am very happy.
He also needs new school trousers, as he has finally grown out of his M&S age 6 extra long ones. He is 10.