One of the biggest benefits of our flexible material, is that it gives lots of room to grow! Grab a carrying case & strap kit combo to keep your little sunnies safe, and to ensure a better fit on infants or kids growing into larger sizes. Comes with head strap and ear adjuster pieces! For teens and adults, we also have our slip grip ear adjusters which help keep shades and glasses in place if slipping off. Generally, as a guide, teenagers from about 10 years + of age would fit our Young Adult S/M sizes.