They are available from Spotlight Enterprises, an educational publisher. Please note that these plays are part of a complete school curriculum and are not available unless you buy into the whole Spotlight program. My Radio Drama Resources website describes the program and would be of great help in producing your own dramas. I write radio dramas that both adults and children will like. I don't believe you need child characters in a drama for children to be interested.
Radio drama is all about imagination.
My plays let the kids become spacemen and gangsters and cowboys and pirates and crusaders. Kids are great consumers of media, and radio drama is the only area where they can produce something that rivals the big guys. Finding radio dramas for production with children can be a little tough. Also, if you are going to work with a large group of children, you need a slightly different animal. This keeps everyone busy and makes for a lively show.