This is what I found when asking myself that same question:
There is no Minnesota law that states at what exact age a child must be before he or she may be left home alone or left under the care of another child. There are general laws, however, that require adequate and appropriate supervision of children. County child protection offices are required to investigate and enforce that general law. As a result, Dakota County Child Protection, a part of Dakota County Community Services, has adopted a policy, which defines those situations when it will investigate a report of children who may be inadequately supervised.
The policy is as follows:
IX. LACK OF SUPERVISION
A. The decision to assess the reports of unsupervised children will be made in light of the following considerations, according to Dakota County Community Services policy:
1. The maturity level of the children;
2. The accessibility of the parent, guardian, caretaker or responsible adult by phone or in person;
3. The physical or mental health condition of the children;
4. The behavioral history of the children;
5. Whether a young child is using a stove, iron or appliance which poses a danger because of their age;
6. Whether the parents have discussed an escape plan or held a fire drill with the children;
7. Whether the residence has a smoke detector;
8. Whether there are unusual hazards in the home;
9. The children's reaction to being left alone;
10. The ages of the children being cared for;
11. Whether the child has completed a Baby-sitting Clinic; and
12. The reliability of the person that the parent has chosen to provide supervision.
Section III. O-17
B. Considering the above factors, the following reports will be assessed:
1. Reports of children 7 and under left alone for any period of time
2. Reports of children ages 8 and 9 who are alone for more than 2 hours
3. Reports of children 10 through 13 alone for more than 12 hours
4. Reports indicating that children 14 to 17 are unsupervised while parents are absent for more than 24 hours will be screened, considering adequate adult back-up supervision.
Hope it helps!
J.