Preschoolers have difficulties in relational reasoning tasks, which are usually attributed to their object focus. Object focus can be reduced by using basic shapes familiar to children and could differ across children. Therefore, in Experiment 1, we investigated 25 4-year-olds' performance in the relational match-to-sample task (RMTS), using basic shapes with training, and testing sameness and difference. In Experiment 2, 41 4- to 5-year-olds were tested in the RMTS, using basic shapes, manipulating familiarity, without training, and testing only sameness. We also investigated whether children's use of object property words (e.g., color, shape) was directly associated with their performance. Our results showed that children performed above the chance level when tested on sameness but not on difference (Experiment 1). Furthermore, basic shapes but not familiar shapes enhanced preschoolers' performance in the RMTS (Experiment 2). Children's use of object property words dampened their performance. These findings underline the importance of task- and child-related factors when investigating children's relational reasoning in particular and cognitive performance in general.