I guess the parent who “helping” their children should be equipped with good enough knowledge in Chinese firstly.
The reason why I saying that is sometime our common used Chinese has already negative impacts on the student who learning them. For example, “这条毛巾3块才” －which is we always say so. Unfortunately this directly translation from English – “this towel costs 3 dollars only” is too literately and not fit standard Chinese order. In another word, it should be “这条毛巾才3块”.
A bit out of your question.
Suggest to look for Chinese native speaking person to do the tutoring.