This study investigates relational reasoning in preschoolers using the Relational-Match-To-Sample (RMTS) task, which tests their ability to match "same" and "different" relations. We investigate (1) whether 4-year-old children can succeed in the RMTS task and (2) whether verbal justifications of relational language predict success. Forty-nine children participated (Mage=54.97 months), and their performance was measured both behaviourally and through eye-tracking. Results show children identified relational matches above chance. Children who used relational language selected relational matches more often. Eye-tracking data revealed distinct temporal looking patterns during relational and non-relational choice trials, with children preferring relational matches after a brief comparison phase. A cluster-based analysis confirmed that children looked longer at relational than non-relational matches. These findings suggest that relational reasoning in preschoolers involves a dynamic comparison process, and eye-tracking provides valuable insight into this implicit cognitive process.