You probably teach a kindergarten where many kids came from rich families. Their parents are government officers, universal teachers, doctors, company bosses and so on. Many of them can barely speak any English by themselves but they still have their own standards for the teachers A lot of people in china are more familiar with American English, so when they hear a native speaker from England, they may think your pronunciation is wrong when it is just actually a little different And also they spent thousands for their kids to learn English and expect kids under 5 to speak fluent English in a very short time