It should come as no surprise that the most important factor in college admissions is grades in rigorous courses. So unless your student is going to be a recruited athlete or an actress on Broadway, extracurricular activities should never trump academics when it comes to ensuring that your child is the most competitive applicant for college admissions.
Unfortunately, you really won't know how far your child's talent will take him until much later in his high school career. And, you should always keep in mind that your star athlete might tear his rotator cuff junior year and have nothing to show on his record but low grades, an easy course load and sub-par test scores.
It baffles me when families come into my office with their thespians and musicians in tow, asking if colleges keep in mind a student's heavy extracurricular load when determining a student's chance of admission. No college admissions officer in his right mind is going to tell you that your kid's long hours in the pool will excuse average grades and a decision to take four classes his senior year.