Your plan's feasible. What's to consider is where you are and who you are to teach in China. Areas around the nation vary in sense of earnings/costs and skills of kids which is what you'll have to think of when setting your courses/lessons, tuition fees and even times per week. Keep in mind that too many locals think lowly of us regardless our qualifications and experiences! Most of the time, parents expectations are unparallel to ours which is why it is important to know your community. To my knowledge, majority of Chinese parents of such little kids want to prepare their little pumpkins for the Chinese primary schools that have some ridiculous English books to say the least. Anyhow, if I had 4 such kids and parents gave me all the time and authority to the education, I'd charge them at least 200 Yuan hourly per child via payment you've well suggested.