Taking computer science and math summer classes for engineering as an incoming freshman undergrad?

If you are planning to take these extra classes for the sake of UCLA, alone, I recommend you not to do that! Do not invest emotionally (and materially) too much on something which is far from certain. If taking those classes would have increased your chances of admision, I would have said to you “go ahead”! But taking them now, only makes you emotionally more attached, which could hurt you at the end!