DS1 is 7. He has long legs and a very skinny waist. M&S age 8 trousers are the right length for him, but are way too big around the waist. They have an adjustable waistband but he finds them uncomfortable if they are pulled in as the button and elastic rub. He can wear them with a belt, but they look a bit bunched up IMO.
Is there anywhere that sells inexpensive skinny boys' school trousers?