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xkcd #2839: Language Acquisition
(xkcd.com)
A community for a webcomic of romance, sarcasm, math, and language.
Vocabulary presumably means learning the meaning of something, which means the parents must have been pretty dedicated in teaching the child the word "twelve" without poisoning their mind with knowledge of how to say any other numbers.
Alternatively, that child has learned twelve words today.
Not to mention the small things in life, like "vocabulary" and "update".
Or the kid has 12 fingers.