An adult yoga teaching qualification isn't a requirement. Please only take the training if you are a yoga practitioner though.
Teaching kids yoga means demonstrating yoga asana (postures) safely. We strongly recommend that you do yoga yourself though, even if you don't have a teaching qualification.
For what it's worth, many of our students are adult yoga teachers (RYT-200 and RYT-500 in some cases) but this is not essential. Many of our students come from teaching or are parents or simply love being around kids - but all practice yoga themselves.