In Michigan, are there any laws against riding two people on a one person snowmobile?

The last time I spoke with the DNR...NO! There was not. There is a law that ATV are rider only and NO PASSENGER. Which they will have to adress with the new line of ATVs out.

If you are asking to ride a kid, most law enforcement won't give you a second thought. If you are riding two grown ups, be prepared to be stopped. Not for a ticket, but to see if you need assitance (broken down sled back on the trail, etc.).

FWIW, my phone call was last January to a women by the name of Jackie in the Law Enforcement Division of the DNR out of Lansing.

Usually on sleds other than two ups, there is a sticker or warning of some type that indicates "operator only, no passengers"

Children should not be a problem as long as you're not driving recklessly. If there is another adult on board with you, then the DNR may write you a citation.