Baby Pokémon
Baby Pokémon were introduced in Generation II as a pre-evolved Pokémon, that is to say, they were added before the original Pokémon in the evolutionary chain after the Pokémon had already been introduced.
Their evolutions mainly center around having a raised Happiness.
Baby Pokémon all have one thing in common: they are unable to breed unless they evolve into one of their higher forms. In addition, until Generation IV, they were not found in the wild with the exception of Wynaut.
In Generation III and Generation IV, new Baby Pokémon can only be obtained by attatching an Incense item to the parents and then breeding them, to explain why they could not be obtained in previous generations.
About half of all Baby Pokémon are part of a three-stage evolutionary line, that is, they evolve again after evolving from their Baby form. Only one of these, however, is achieved by level up, with most of the others requiring use of an evolutionary stone or held item to evolve a second time.
Baby Pokémon were eventually introduced in the Trading Card Game as well.
This is a list of Pokémon which are classed as being babies:
Togepi may or may not be classed as a baby Pokémon, because when it was introduced in Gold and Silver it was not a predecessor of an existing Pokémon. However, due to its especially baby-like manner as depicted in the anime, as well as its inability to breed, it is assumed to be a baby Pokémon. This is also true of Riolu, which was introduced in Generation IV along with its evolution, Lucario.