Does the semen contained in each ejaculation represent hundreds of millions of different children?

You are what you are now because this process is unrepeatable, that is, there is no way to prove or falsify it. In theory, the combination of two absolutely identical sperm and eggs will produce exactly the same offspring. The similarity here is only physical similarity, not to mention mental consciousness, which is also influenced by acquired experience. Even if we only discuss the body, the genetic information contained in the sperm of the same person is mostly the same, which is why we are all human beings, but there are also a few differences. There must be physiological differences between several children of a man (regardless of identical twins). This is because sperm cells undergo meiosis, and half of the genetic information contained in your body comes from your father and half from your mother. They should also know something about these contents after learning biology in middle school.

Your first sentence, if hundreds of millions of sperm of the same man are fertilized successfully and develop into a fetus, there are really no two physically identical, because the variables of genetic information are far more than this number. Two sperm with exactly the same genetic information were found, but they were not zero in theory, and the probability was unknown how many times as negative as 10.

In your other words, we all came to this world with a probability of one in hundreds of millions. I think it can almost be said, but it is more accurate to say that "you" cannot be equated with successful sperm, because the generation and growth of human consciousness are absolutely unrepeatable. Suppose there is a person with exactly the same body and perfect growth experience, you can't be the same person with him. Your thinking and behavior must be random.