The birth of a human can change many things in history of mankind. For example, Louis XVI and Louis XVIII will have to spend some time differently (even if the major part of the education is done by other nobles - then again, those occupied with the education play a different role in the following years). Maybe Louis XVIII's son will be affected of the same disease as Louis Joseph, Louis XVI's first son?
Sure, the Revolution will still happen, because, as you said, "Well how could the birth of the boy stop the French Revolution? Is his birth going to allow for reforms to go through when otl they were blocked, and if so why?"
But then the butterflies start to strike. "Is his birth going to stop the storming of the Bastille? If so how?"
The people of Paris did not storm the Bastille on a whim. It had specific reasons you can read
here, reasons which would not unconditionally exist if Louis XVIII had a son - maybe as a father, he would advice his brother to be more careful? Or, au contraire, he his even more reactionary than OTL and the storming of the Bastille is more bloody? So the revolution becomes radical much faster than OTL?
"Thirdly how would he able to stop the rise of napoeloen?"
It cannot be ruled out that Napoleon will still rise very high - the birth of Louis' son will not remove his military talent or his ambition. But it will not happen under the same conditions than OTL. And you can be sure that the year 1814 and the return of the Bourbons, if it happens at all, will not be as OTL.