Baby

Babies were what humans called their young. In general, human offspring were referred to as babies from birth to approximately when they began to walk. According to the Eleventh Doctor, babies had their own language, which he could speak. (DW: Closing Time)

The fleshkind baby, Sky Smith, was primed to rapidly age into a pre-teen upon encounter with the metalkind. (SJA: Sky)

Babies encountered by the Doctor

 * Audrey Dudman (DW: The Curse of Fenric)
 * Ace (ST: Ace of Hearts)
 * Rose Tyler (DW: Father's Day)
 * Melody Pond (DW: A Good Man Goes to War)
 * Alfie Owens (DW: Closing Time)