Vicky's Little Brother is an unnamed, unseen character that was only referenced once in the entire series, in the pilot episode.
When Vicky first started babysitting Timmy, she threatened him with blackmail, stating that it works great, "Just ask my little brother!", she picks up and dials the phone to her house, and her brother is heard screaming for a few seconds before she hung up. The next time Vicky's House is seen however, she only has a little sister, Tootie, and her little brother was nowhere to be seen. This character has yet to appear in the main series and is now considered a nonperson.
Reasons for removal
The pilot episode has many elements that were contradicted in later episodes. Timmy's exact meeting of Vicky and his fairy godparents was different in "Abra-Catastrophe!". This is because the pilot episode was made more in mind with getting the show picked up for more episodes, and when the creators succeeded in this, they decided that certain elements were worth changing, such as making Vicky's younger sibling a girl in love with Timmy.
In every episode, book, comic, and video game that Vicky's entire family has appeared in, her brother is not seen or referenced once, which means that the creators have established that he does not exist in the main series. He might even be deceased, but their is a much more valient explanation, which might Vicky might have been referring to Tootie instead of her brother in the Pilot Episode, as the screaching is mostly from a girl, revealing that Vicky's little brother might have been Tootie off screen, at the time, and that Vicky actually lied about having a brother.