回复：目前就是有点担心孩子的学习能力，估计勉强够MIT的水平，怕压力太大

1. Should not worry about your child's ability if mit would admit him. Trust mit's judgement, as they are usually so good at it;
2. Many students in mit (as well as in other elite colleges) regularly spend good amount of time in sports of various levels, or in other ECs. Your child seems to have the capacity to for rigorous class work and still have room to pursue other personal interests.  I would trust him and let him try it. Who knows where your son's limit is, before he tries it!
3. As a mit student should have a good chance to transfer, in case he wants to make an adjustment later.