The dance teacher of children and young people has the task of not only teaching syllabus, honing technique and sharing the basics of a complicated and varied art form; they also have a responsibility for the physical development of the students under their instruction. This goes for any genre of dance, from ballet and contemporary to hip-hop and bhangra. In fact it goes further than that, it goes to any professional working with young people in any physical discipline - from dance to martial arts to athletics. The student is essentially at your mercy.
You tell a 10 year old their body should be able to do something - they will see you as a figure of authority and take you at your word. You're meant to know best. That's all well and good when you do, when you are aware of the physical abilities and limitations of the students you work with. When you don't it becomes problematic. It is your responsibility to develop your own knowledge, and to then find a suitable means of transferring it to your pupils.
You don't know anything about physiology? Study it. Anatomy? Learn it. Nutrition? Read up on it.
Knowing how to perform every step is not enough, knowing the syllabus is not enough, having perfect technique yourself is not enough. Teaching is a vocation, it is not merely a job. You need to understand your students' bodies in order for you to help them to get the most out of them. On a basic level this means understanding everything from childhood physical development through to adolescence or understanding the effects of nutrition and eating disorders, on a more in depth level it means developing your knowledge of any specific conditions your student may have. If a student starts with you who suffers from arthritis, or asthma, or epilepsy, and you know nothing about it - learn about it. Perhaps they have learning or developmental difficulties. Learn about it. Learn what effect this may have on their physical performance, on their physical development, on their neuromuscular control. Teaching does not mean you can use a one size fits all model to impart knowledge. Every student is different, their bodies are different, their psychology is different, their abilities and their strengths are different.
Teaching is more than blindly reiterating what you were taught as a student. It is more than steps and syllabus and perfect timing. You are teaching a physical art form, therefore you need knowledge of both the physical body as well as the art form itself. You should always be developing yourself as an artist and as a teacher, the two go hand in hand. The more you understand about the individual and can adjust your teaching techniques as needed, the more your students will get more from your classes, and the performance they are capable of will improve dramatically.