The aim of this study was to evaluate the differences on motor competence between boys and girls aged 4 years old and investigate the existence of Relative Age Effect on their motor competence. In total, 132 preschool children were evaluated, of whom 60 (45.50%) were girls and 72 (54.5%) were boys. The distribution of the participants was from quarter 1 [n = 28 (21.2%)], quarter 2 [n = 52 (39.4%)], quarter 3 [n = 24 (18.2%)], and quarter 4 [(n = 28 (21.2%)], respectively. The Movement Assessment Battery for Children-2 (MABC-2) was used to collect the data. The data show the main effects on quarter of birth factor in manual dexterity (MD; p < 0.001), in aiming and catching (A&C; p < 0.001), in balance (Bal; p < 0.001) and in total test score (TTS; p < 0.001). There are also statistical differences on gender factor in MD (p < 0.001) and in TTS (p = 0.031). A significant effect was also found in the interaction between two factors (gender and quarter of birth) in MD (p < 0.001), A&C (p < 0.001), and Bal (p < 0.001). There are differences in all the variables studied according to the quarter of birth and only in manual dexterity and in the total score if compared according to gender (the scores are higher in girls).