Criminal Law Questions? Ask a Criminal Lawyer.
Yes, the police can interview anyone they choose to in the course of an investigation. Not only can the question and interview minors, they do it all of the time during investigations. There is no law, contrary to the amazement of many parents, that states that social services or the police must have a parent's permission to question a minor. As long as they have grounds to question the minor they may do so. However, once a minor is represented by an attorney, the minor may not be questioned without the attorney present..
As far as the police questioning the minor without an adult present, while the police can do so, any actual statement obtained but not taken by the police in the presence of some independent advocate should not be admissable in court.
As long as the parent confirms that they did give consent for any questioning to occur without them being present, in any legal or administrative proceeding the minor's statements are admissible. If the parent did not consent, there would be grounds for trying to get the statements excluded.