I have encountered the same problem and have hence stopped recommending my young students to visit open ESL chatrooms without being supervised by myself or their parents. Here, education about on-line sexual predators should be enough of a warning to students.
I have been providing a service for a few years now where anyone can come to my on-line school and talk to me while I am working on-line. I utilize SSL encryption and I try to make the experience as interactive as possible. I can also follow and monitor students' progress while they are on my web site. The secure environment installs a trust in my students that they don't find in open chatrooms and I find more and more return customers outside my classes.
I also have made virtual classrooms where I put them behind secure subdirectories in my on-line school which are password protected to eliminate the arrival of sexual predators and in general have the power to ban or suspend any visitor when I deem it necessary while teaching outside my own on-line school.
Feel free to visit me when I am working on-line.
Eric Paul Monroe