Whatever you do, keep an eye on your kid or have them ride with someone that knows what to do in case of a bad situation. I can't tell you how many times, even on these small MI hills, I've seen kids under 10 getting hurt with no one around knowing what the heck to do. I also see youngsters doing shit they shouldn't like trying to ride down a wall of ice/grass that transitions into fast runs where they have no business being on.
I'm not saying be super strict here, just to be responsible about it. Me personally, I wouldn't let my son ride alone because I want to be able to help him if he gets hurt. Ski patrol doesn't always do a good job (as I've also witnessed many times).