What is the minn law on decision for a child not to be with the other parent? My grandson is 11

The child doesn't get to decide anything until they are 18. However, a child's preference is given more consideration the older the child is. Please see THIS (http://www.divorcehq.com/faq/mn-divorce-faq.shtml#Custody0) link.

what is the minn law on decision for a child not to be with the other parent? my grandson is 11

As already noted, the child cannot make that decision - the final say is left up to the judge.

Could you give us some more information regarding the situation? Does your grandson want to move or are you merely asking out of curiosity?

The preference of an 11 year old is not likely to be given much weight. But if the non custodial parent wants a change of custody they have to file for a modification, present their reasons including the child's testimony and see what the court says.