Parents are pushing extracurricular activities at an earlier age all the time. Infant swimming lessons, preschool gymnastics and soccer, and music or art lessons before they can add or subtract are becoming the norm!
A child’s extracurricular activities should be of their choosing (within reason), i.e. something they have developed an interest in. Infants and preschoolers do not have the mental capability to make those kinds of choices.
Children in this age group generally may not possess the physical strength and stamina needed for such activities, the mental clarity to comprehend the rules of a game, and the ability to focus for the amount of time required by such extracurricular activities.