In Vampire: The Masquerade and Vampire: The Requiem, a neonate is a recently embraced vampire that has as passed through the initial stages of vampiric existence, the fledgling stage. It is the sire's responsibility to ensure that the childe does not embarrass itself or its sire in vampiric society. Derogatorily, a neonate is often called a whelp.
Neonates are generally lightly involved in the true machinations of undead society. They aren't powerful enough to really matter, and are consequently used primarily as pawns by their elders. Conversely, they still have an investment in the mortal world of the 21st century and are less likely to adhere to the feudal character of vampiric society.