Just search it in Google, it will display you some sites that provide semi rimless glasses for children. As far as i know, eyebuydirect.com, myglasses.com, and more sites that offers eyeglasses for children (including semi rimless glasses). Before you buy eyeglases online, you must prepare well your kid's prescription and know her/his frames sizes so as to get proper prescription semi rimless glasses. Hope this will help.
Many opticla stores also offer kids glasses of different types. Just take your child to back to the place where you bought them full frame glasses. I believe every optical stores have semi rimless glasses sold. If the prescription of your child has changed, he will be asked to have an eye exam again and then you can help him to select the semi frame glasses for him. Or you can search semi rimless glasses online and order them with the new prescription. There are many online optical stores offering semi rimless glasses for children.