What leads you to believe that Brutus was the son of Caesar? I'm curious to see where you received this notion from.

As far as we know, the only biological children of Julius Caesar were his child with Cleopatra who was killed in infancy, and his daughter Julia that died during childbirth.

Even non-biologically, Caesar is only known to have adopted Octavian.

Brutus was certainly close to Caesar, but was never his son in any way.