A senior officer with Hampshire Police says it "might take a bit of time" before the King family return to the UK after they travelled to Spain with five-year-old Ashya.
A group of officers will travel to the Spanish city of Malaga to speak to Brett and Naghemeh King about why they took their son from a hospital in Southampton.
Assistant Chief Constable Chris Shead said the Kings could return to the UK "reasonably quickly" but past experience "suggests it might take a bit of time".
The head of the police force which applied for a European Arrest warrant against the parents of Ashya King has now urged their release.
A British mother whose son's life was saved by proton therapy has told ITV that she defied NHS doctors' advice to pursue the treatment.
The parents of Ashya King said they took him out of a hospital to seek proton beam treatment which is not available under the NHS.