There is a certain wisdom in not teaching spellcraft to children. As a member of one of the traditional paths, we have our one basic rule that we do not teach children as part of our teaching.
That said, if one is intent on teaching the craft to their children, then it is IMPERATIVE that the child be fully aware and responsible for their actions. There is no safe practice for an irresponsible witch.
The best thing to do is to teach them ritual and discipline.
Make them do homework as to the reasons behind each ritual and each action behind the ritual and make sure that they fully understand about intent and consequences for actions.
Focus on the Sabbats and esbats to start with, and later you can work on teaching simple healing spells as they become ready to do such work, such as accelerating healing of small wounds and things of that nature. And always teach focus and be sure that they are ready for the work that they are entering into.
And teaching should be done in stages, just as it is with adults. No effective witch ever started with the complicated things; they always started with the absolute basics and worked their way up to the more complex things, just like in mundane school courses.
Shawn May Scott has made some very good points on this subject that I do not need to repeat.