Can my daughter keep their son away from his dad if he says he is going to smoke pot

Lawyers.com offers general information and not legal advice. You are seeking legal advice, which cannot be provided without additional information.  First, are there any court orders in place?  If so, do the terms spell out the rights and obligations of each parent, as to visitation with the child?  When you say, "can she keep the son from him until they go to court..." you do not say why she is going to court.  Is she going to court to modify an existing court order? If so, is this an emergency proceeding? If neither of the referenced situations apply, is the mother going to court to ask the court to enter an initial court order, defining the rights of the parents? Your question needs to be specific, because the answer will change, depending on the facts in the case.  Therefore, it is recommended that you confer with an experienced family lawyer to discuss this matter in greater detail.  Best of luck~