In contrary to the publicly known word "theory" doesn't the scientific theory mean a guess. An idea, a guess or better, a claim would be a hypothesis. A theory would be a proven hypothesis. Also, prove is a far more powerful term than for instance in law. A prove is not only swept away. So, proves are actually final. That's a problem, by the way, because we did correct proves before by finding out mistakes and therefore realising it was never proven. But evolution is one of these things that is actually proven quite well by fossils, embryology and genetics.
So that's why you are proposing a hypothesis and not a theory.
After that's clear, let's take a look on your hypothesis. You are taking the premiss that babies are brain dead for quite some time. That's actually not true. Their brains are fully operational. They just need some time to learn. This can be easily shown by EEG. Your premiss is wrong.
After your premiss is corrected, let's take a look at the rest. The body as an empty vessel for the soul? Okay, if that's the case, the sould can be harmed by a knive. Since brain surgery can cause any number of damage, like amnesia or hallucination, that knive must have hurt the soul. If that's the case, we should all be brain dead. So many violent death with brain injuries. Our souls must be so damaged that we can't even think straight anymore. But that's obviously not the case, so souls can't be damaged by knives. But since we can cause damage with a knive to our behaviour patterns, we can't be controlled by that soul.
Therefore, your hypothesis is falsified. That means, it's proven wrong. But nice try. Try to structure your hypothesis into premiss, claim and possible prove next time, okay?