Children are really active ones, they don't care much about their eyeglasses, such as sitting on them or over bend them, thus the frames and lenses can easily go broken and scratched, so what's the best lenses for kids eyeglasses?

That`s true ,so I suggest young parents to buy plastic or PC lenses which are not fragile and durable.

I couldn't more agree with that, PC lenses are do the best choices for kids eyeglasses, they can not be scratched as other kinds, I just suggest you to choose AR-coatings when buy PC lenses, they can help you to eliminate the glare reflected from the lenses thus provide you a more clear vision!

Yes, PC is good choice.

Actually, Polycarbonate is the lightest, most impact-resistant material made. With an index of refraction of 1.61, polycarbonate is thinner than standard (CR-39 optical resin) optical lenses. Say "goodbye" to the heavy bifocals that put little dents in your nose; these barely feel like you're wearing glasses at all. As the safest material available, polycarbonate is ideal for bifocal wearers with an active lifestyle or for those who have one eye that is much better than the other (amblyopia), so your good eye is always protected.