Do you know the material used for flexible frames for kids?

[Emmanuel Eyeglasses]

I have visited a local optical store today and I was overwhelmed with the pricing, like OMG!!! the prices go crazy high up. I was shopping for a kids frame because my 3 year old usually bends and breaks his pair, I was recommend a flexible frame, like they bend and unbreakable, is this safe for my 3 yr old and what type of material is being used?