The sentence you wrote is almost correct, but it can be made clearer with a slight change. Here's a better way to say it:
"The brain has two halves: the left side and the right side. Each half controls the opposite side of the body."
Explanation:
- We don’t need to capitalize 'brain' unless it’s at the start of a sentence.
- Using "half" instead of "side" in the second sentence makes it clearer that each half is responsible for the opposite side of the body.
This makes the sentence easier to read and understand.