Baby Language

"Craig: He's called Alfie. Baby Alfie: [gurgles in Baby Language] The Doctor: Yes, he likes that, "Alfie". Though personally, he prefers to be called "Stormageddon, Dark Lord of All"."

- Doctor Who, "Closing Time"

Often in fiction, babies who can't talk yet are treated as having their own esoteric language, similar to Animal Talk. Adults can't hope to understand this language without magic or phlebotinum, yet it's usually understood by all babies regardless of national origin. Usually this will be the center of the plot for that particular story, although it may occasionally be used as a throw-away-joke.

Whether the babies have an intelligence to match their language varies greatly. In some works it may just be a cute-sy version of Hulk Speak. In others the babies may in fact be geniuses, and unable to share their brilliance with the world -- what a shame they forget it as soon as they begin to actually communicate. In others the children seem to be relatively intelligent, but with poor decision skills and naivety, making them less capable. This last one is usually the most successful, but any of these forms can result in awkwardness if not handled well.

Creepily, this might have an element of Truth in Television. Studies show that babies actually understand far more words than they’re actually able to speak because they’re so uncoordinated. It's called passive vocabulary. Imagine being able to understand what’s going on around you, but all you’re able to do is cry and flail.

Comics

 * One Baby Blues strip revealed that Hammie (at the time a toddler) could perfectly understand his younger sister Wren's baby talk, as well as speaking English. Zoe (a kindergartner) observed that she must have grown up too much as she couldn't make any sense of baby talk anymore.
 * This was the premise behind Sheldon Mayer's classic comic series called Sugar and Spike, that all babies, no matter what species, spoke a universal "baby language".
 * Sugar and Spike appeared in one issue of the Batman the Brave And The Bold spin-off comic (which appears determined to not only have dafter plots than the series, but even more obscure guest stars). Batman gets turned into a baby, and can instantly understand them.
 * GLX SPTZL GLAAH!

Film

 * Baby Geniuses
 * Look Who's Talking had some of this.

Literature

 * In P.L. Travers' original Mary Poppins stories, babies could talk to each other.
 * In A Series of Unfortunate Events, toddler Sunny spoke in subtitled gibberish. Her speech was translated in the books.
 * Apparently, in Diary of a Wimpy Kid, Manny knows several toddler slang terms. The only one we hear is "Ploopy," which Manny apparently considers quite offensive.

Live Action TV

 * Doctor Who: "A Good Man Goes To War" reveals that the Doctor can apparently speak baby. His companion doesn't buy it, and he calmly retorts "I speak everything". With the translation circuits, this may actually be true.
 * Back once again in the episode "Closing Time", where the Doctor spends much of the episode translating a baby for his father, Craig. Incidentally, the baby calls Craig and the Doctor 'Not Mum', everyone else Peasants and himself "Stormageddon, Dark Lord Of All."
 * At the end of the episode that all changes. (Also, despite the Doctor's efforts to seem like he never appeared, Alfie's first actual spoken English word is Doctor.)

Western Animation

 * Rugrats is an interesting case in that three-year-olds like Angelica and Suzie can talk with the baby characters as well as with the adults.
 * Kate from Arthur did this. However, she could talk to Pal, the dog, implying that her Baby Language was on the same level as Animal Talk.
 * Stewie on Family Guy may be an example, depending on how the writers feel that day.

Real Life

 * As mentioned above, babies do acquire a huge amount of passive vocabulary. Some psychologists recommend teaching babies to use sign language beginning at about nine months.