I was never able to work at an early age, as I was always in a boarding facility where pupils and students can only do as their told.
However, work ethics is something I will very much love to teach my children, because I know first hand the effect it causes as an adult.
Your nephew is one lucky kid.
Work ethic is certainly important and it can be taught or acquired in many ways. If you have a think about it, I'm sure you'll come up with some excellent ways to teach your kids and when they're adults and their lives are their own they'll thank you for it.