It depends. Generally speaking, police need probable cause that a crime has been or is being committed in order to lawfully search a motor vehicle without consent.
Is there a criminal case pending against anyone? Did the police offer any reason for the search?
If the search of the car produced contraband that resulted in criminal charges, then the defendant in that criminal case may have standing to contest the search of the car.
The police may also argue that given that the car was inhabited by a group of unaccompanied minors, they were performing a community caretaker function by searching the vehicle. However, the real question is whether or not it is a moot point that the police searched the car: if they did but no consequences resulted, then don't worry about it.
If one of the occupants or the owner was charged with a crime, either provide more details about the case or speak to a criminal defense attorney.