I've found that children aren't very receptive to feedback unless you have invested the time to have a really good relationship with them. You can tell them about good habits, honesty, etc; but if they lack the will it is useless. You need to have fun with them and have conversations where you don't put any pressure on them - just let them be their honest selves, and talk about anything they are interested in. After that you can have more fruitful discussions. That's my experience. In any case, it's incredibly interesting and challenging!