The UV rays in sunlight can be harmful to your young eyes. Lenses that block 100% UV help to ward off various eye conditions and damage.
Scratches on lenses are, plain and simple, distracting, and they can interfere with lens performance. Scratch resistant treatments imbued into the lens surface toughen up the lens making them more durable.
For fashion, comfort, and clarity anti-reflective treatments are the way to go. They make the lens nearly invisible and cut glare from the headlights, computer screens, and harsh lighting.