Hocosa Big Boys Organic Wool Long-Underwear Pants Made of soothingly soft European KbT-Certified Organic Merino Wool. Natural fibers breathe, maintaining a comfortable temperature in warmth or cold. Wicks moisture away from skin, keeping your child warm & comfortable. Even when wet, wool feels warm. Natural wool with lanolin gives self-cleansing properties for easy care. For best fit - European size correlates to child's height in centimeters. Child's height in inches x 2.5. For heftier children or room for growth, go up one size. See Product Description below for sizing guide.