I ordered a size 10 slim and they are perfect. My son is 10 years old 70lbs, slim and 4' 10" Normally he fits an 8 with an adjustable waist but the length is always too short. These are perfect, even have a little extra length and no need for waist elastics (which they don't have) One more thing, they are not bright red like the photo, more of a muted burgundy red, a great color for boys.