Well, in my opinion, you can just choose Polycarbonate lenses which are well known to be safer and thinner but rather lack optical clarity. And it can be a good choice for your kid. First, you should know that Polycarbonate lenses are also known to be thinner and lighter than traditional type lenses. Polycarbonate lenses offer total protection from UV light and radiations. On the contrary, ordinary plastic offers minimum protection from UV light. If your kid use plastic lenses, you may need to invest in antiglare material to protect your kid from any harmful rays. So in my opinion, you should choose Polycarbonate lenses for your kid. And this kind of lenses is durable.