Potential energy increases because the train moves against the magnetic force.
Explanation:
When the magnetic toy train is moved away from a magnet that cannot move, the potential energy in the system of magnets during the movement is affected as there's an increase in the potential energy because the train moves against the magnetic force.
We should note that the potential energy simply means the energy that is stored in the magnetic toy. Since the magnetic toy has been moved away from the magnet, the likelihood of its attraction will reduce thereby there'll be a rise in the potential energy.