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".
Ashya King's parents told the Daily Mail they fled the UK after being told NHS treatments would leave him with life-long disabilities.
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.