Daughter was arrested for not reporting to her probation officer . They took her child's phone and will not return until they open it ,I'm the grandmother who have the kids can she keep it? Can she request it to be opened before returning?

The phone was in her possession, The parole department can do anything they want if there is a legal cause. Who is paying for the phone, the child, most likely if it is a younger child, mom or grandma is paying for it, so it is not really the child's phone.

But merely give them the code to open the phone and allow them to check it, and then they can return it. (unless there is things on the phone, that violates the parole)

Some people on parole for example can't have phones