From Next! They are the mid wash jeans code 37-843-380
They are made with a double turn up at the bottom but its only lightly sewn up and not pressed or anything, so you can get the waist size that fits your DS, un pick the turn up and you have extra long length jeans!
My DS wears 2-3 waist but I usually have to get age 4-5 for the length, so these are perfect for nice fitting jeans rather than very very baggy!