You have a right to the presence of your legal guardian once you are under arrest, and the process is not immediate. You can't demand your mothers presence in the back seat of a cop car. You can at the station though, for example.
You don't have the right when you are in the process of being arrested, especially if you are actively resisting arrest.
You don't have the right when you are in the process of being arrested, especially if you are actively resisting arrest.