Frames for children are made of plastic or metal, and many styles are intended to mimic unisex frames designed for adults. Kids are often drawn to these styles because they look more grown up. It's not uncommon for children to choose to look like their older siblings or the glasses their parents wore.
In the past, plastic frames were a better choice for children because they were considered more durable, less likely to bend or break, lighter, and less expensive. But now, manufacturers are also making metal frames that incorporate these features.
Metal compositions vary, so ask your optician which one is best for your child based on experience with different alloys. If your child shows sensitivities to certain substances, choose a frame made of hypoallergenic materials.