What is the test for a motion for summary judgment against a parent for failing to supervise their 17 year old son's birthday party?

The plaintiffs rely on the case of Oyagi v. Grossman, [2007] O.J. No. 1087 (S.C.J.) in which the court dismissed an application for summary judgment when the teenaged son had sent internet invitations to a party at which beer would be served and which resulted in a party involving a “riotous and disorderly group”. In the course of the evening the numbers grew to approximately 100 and thefts began to occur. At one point a thief was pursued who got into a motor vehicle and drove forward injuring the plaintiff. The motions judge found that the defendant parents owed a reasonable duty of care to those coming into the property when they left their 17 year old son with a minimum of oversight, having warned him that he should not hold a party, that they should have been reasonably aware that he would disobey their instructions.