Compared with plastic lenses of eyeglasses, the material of polycarbonate eyeglasses is durable and strong. However, this type of eyeglasses is too heavy for the kids which may leave the nose print. You'd better choose the plastic ones which may let your kids feel comfortable. You should take many elements into consideration.
The best material of glasses for child is resin. It is more safe and light for the burden of their nose bridge. The resin is the lightest material for the glasses make. The glass material is fragile to broken. The glasses without nose pad will be more comfortable for kids. All the glasses frame is a integral part, this kind of glasses are more likely to suit kids. Moreover, the contacts lenses will not suit kids also. It's hard for them to keep it clean and easy to be broken.