The purpose of this study was to evaluate whether a Relative Age Effect (RAE) exists in motor competence of preschool children. The hypothesis was that motor competence, assessed by the Movement Assessment Battery for Children-2 (MABC-2), would be higher in preschool children born in the first quarter of the year compared to those who were born in the last quarter of the same year. A total of 360 preschool children were evaluated of whom 208 (57.8%) were boys and 152 (42.8%) were girls, with a mean age of 4.52 years old (± 0.50). The distribution of the participants was 172 children aged 4 years old and 188 aged 5 years old. The data showed a main effect on the age factor in the total score of aiming and catching (p < 0.001) and in the total test score (p < 0.001), in the quarter of birth factor in all the dimensions studied (i.e., total score of manual dexterity (p < 0.001); total score of aiming and catching (p = 0.001); total score of balance (p < 0.001); total test score (p < 0.001)) and in the interaction between both factors (i.e., total score of manual dexterity (p = 0.005); total score of aiming and catching (p = 0.002); total score of balance (p < 0.001); total test score (p < 0.001)). Age and quarter of birth produce a RAE in 4 and 5-year-old preschool children’s motor competence.