Polly says it was by magic, and when Digory agrees she figures that herrrs not a magician, but has traveled on another's magic.
It was at this point in their young life's that they took far more prolonged interest on s (uppers, prellys) or a German made pills called "Preluden. https://medea.medianet.cs.kent.edu/mediawiki/index.php/Eskort_Ar%C4%B1yorum_Diyarbak%C4%B1r